Transmission Adapter Kits For Domestic Engines From US Shift

If your build has ever hit a wall because your engine and transmission simply were not designed to talk to each other, you already know how expensive and complicated that problem can get. US Shift has partnered with Performance Adapters to offer transmission adapter kits covering just about every major domestic engine family Ford and GM ever produced.

Whether you are running a vintage big-block Ford, a classic GM inline six, or a modern Coyote, there is likely a kit here with your name on it. Every adapter plate is machined from 6061 billet aluminum, and each kit ships with a high-torque mini starter, a crank spacer, and all hardware for installation. Builders who are also purchasing a US Shift controller can contact US Shift directly to bundle the two and receive a discount.

Ford Transmission Adapter Kits

Two Ford engine families covered are the M-block 351M/400 small-block and the 385-series 429/460 series (so named because of their 3.85-inch stroke). Performance Adapters offers transmission adapter kits for both mating to either Ford small-block and Modular bellhousing patterns or GM V8 transmissions.

The Ford 351M/400 to Ford small-block and Modular kit opens the door to the AODE, 4R70W, 6R80, and 10R80. At one inch thick, the kit uses a simple crank spacer to retain the OEM C6 14.25-inch flexplate. That approach eliminates the need for a torque converter spacer and cuts down on potential failure points. Grade 8+ 7/16-20 bolts thread directly into the crank and can be tightened to factory specs. The kit carries a dual pattern for both the small-block Ford truck bellhousing and the Ford Modular V8 bellhousing, giving builders a wide range of transmission options. Note that this kit does not work with the 157-tooth flexplate.

The Ford 429/460 to Ford small-block and Modular kit follows the same construction philosophy, with the same dual-pattern bellhousing compatibility and the same off-the-shelf starter for easy roadside replacement. Builders who want to run a GM transmission behind a big-block Ford can turn to the Ford 429/460 to GM V8 kit instead, which covers the 4L60E and 4L80E. That kit uses a factory-style flexplate and requires zero bellhousing modifications. Note that 1979-1999 460 engines require a 28 oz. external balance weight unless built for neutral balance, and the 157-tooth flexplate is not compatible here either.

Other Small-Block And Modular Transmission Adapter Kits

The small-block Ford catalog is where things get particularly interesting for classic and restomod builders. The Ford small-block V8 to Ford Modular kit supports engines like the 260, 289, 302, and 351W and opens the door to the 6R80, 10R80, 4R70W, 4R110, and 5R110. The adapter plate measures 0.5 inches thick and requires no cutting or grinding of the bellhousing. A high-torque mini starter rated for up to 14:1 compression comes in the kit, and the crank spacer eliminates the need for a torque converter spacer.

Early Small-Block Ford Five-Bolt Adapter

Builders working with 1961 to 1964 small-block Ford engines have a dedicated option in the Ford small-block five bolt-to-six bolt and Modular transmission adapter kit. Those early 221, 260, and 289 cubic-inch engines used a unique five-bolt bellhousing pattern that is not compatible with later Ford transmission designs. This CNC-machined kit bridges that gap and opens up modern six-bolt SBF and Modular transmissions as options.

For small-block Ford builders who want to run an Ecoboost V6 transmission rather than a V8 unit, that option is available as well with the Ford small-block V8-to-Ecoboost V6 kit. V6 6R80 and 10R80 units are more common and more affordable than their V8 counterparts, and they carry a heavier-duty rear output bearing because the Ecoboost V6 makes more low-rpm torque than the Modular V8. The adapter plate measures 0.5 inches thick and offers 11 possible starter clocking positions to avoid obstructions in the engine bay. It retains the factory torque converter with the 11.4-inch bolt circle pattern, so no custom flexplate or converter spacer is needed. These transmission adapter kits work with the 2.7-liter, 3.0-liter, 3.5-liter, and 3.7-liter Ford V6 Ecoboost transmissions found in F-150s, Mustangs, and other larger Ford vehicles.

For Coyote swappers going the other direction, the Ford Modular to GM V8 kit mates the Coyote to a 4L60E, 4L80E, or 10L90. It features a half-inch billet aluminum adapter plate, an SFI-certified flexplate, and a GM high-torque mini starter. The full Chevy bellhousing is retained and no modifications are required. Buyers select between the six-bolt or eight-bolt crank pattern at checkout.

GM Engine Transmission Adapter Kits

On the GM side, the lineup covers classic inline six and LS engine applications. The GM Inline 6 to GM V8 kit targets the 216, 235, and 261 cubic inch engines produced from 1937 to 1962. These engines appeared across nearly all Chevrolet and GM platforms of the era, and this kit pairs them with a modern 4L60E or 4L80E. The one-piece 6061 billet aluminum adapter plate bolts in with a handful of fasteners and requires no cutting or grinding. A custom pre-welded flexplate works with a three-pad 10.75-inch or 11.50-inch torque converter. Builders should note that this kit uses a standard flat SBC-style flexplate compatible with older 4L60E units, but not later models with the dished flexplate and smaller converter bolt circle.

The GM Atlas 4200 Vortec Inline 6 to GM V8 kit is available for builders looking to mate the Atlas inline six to GM V8 automatic transmissions. It includes a CNC-machined adapter plate, a starter and starter adapter mount, longer hollow dowel pins, a torque converter snout adapter, and all necessary hardware. An optional adjustable intake cam gear is available as well.

For LS swappers running a Ford driveline, the GM LS1/LS2/LS3 to Ford small-block and Modular transmission adapter kit makes it possible to keep the original Ford transmission while dropping in an LS engine. The adapter plate is one-inch-thick 6061 billet aluminum with a 1018 steel crank spacer, and the starter mounts directly to the adapter plate. Depending on the specific transmission, minor material removal may be necessary for starter clearance. These kits primarily target LS1, LS2, and LS3 engines, though other GM engines sharing the six-bolt, 79mm bolt circle crank pattern may also be compatible.

No matter what engine and transmission combination you are chasing, Performance Adapters and US Shift have likely already solved that problem for you. Check out the full lineup, and if you are pairing an adapter with a US Shift controller, reach out to them directly.