One of the cornerstones of car crafting is engine swapping for increased performance, but for years, engine choice has also dictated the transmission to be used. However, over the past decade, a number of interesting overdrive manual transmissions have come to market, and naturally we want to stick them behind our engines, but this isn't always possible with factory parts. Traditionally, hybrid drivetrain mergers have required custom bellhousings or gearbox adapters, but these are usually only available for the most popular combinations.
The main part of the McLeod modular system is referred to as a universal bellhousing, though the universal part is the aft portion. On the engine side, these are still application-specific, though some, like this Chevy/B.O.P unit, cover more than one engine.
McLeod has recognized the need for vast interchangeability of engines and transmissions, not just to mate late-model overdrives to classic powerplants, but also to mix and match components of varying vintage from multiple manufacturers. Its solution is a modular bellhousing system, in which the bellhousing is made up of multiple parts that can be mixed and matched to mate a broad scope of engines with a similarly broad range of manual transmissions.
The basic idea is relatively simple: Each modular bellhousing assembly is made up of four parts: the bellhousing, which bolts to the engine, the "cap," which mounts the gearbox, a spacer ring that sandwiches between the two to establish proper input shaft depth, and a reducer ring that centers the gearbox's input bearing retainer in the cap. All of the pieces are aligned using steel dowel pins, which have eccentric ends so that the centerline of the gearbox's input shaft can be precisely aligned to the crankshaft centerline.