[Cal Metal]

I would assume that the requirements would be for both big in/out as well as small in/out as the Big shaft trannys were restricted to the 427/428/429 engines. The mainshaft diameters are the same for both transmission for the gearing and hubs mounts with the exception of a larger spline for the output in the "big out"(north of the rear bearing) and a larger spline on the input for the "big in"(north of the input bearing). The gearing on the mainshaft interchanges between both transmissions, contrary to popular belief.