Doesn't a 51 3 speed have the oddball small transmission to bellhousing bolt pattern? If he's going to swap to an open driveline he's going to need to change everything from the engine back, including the bellhousing. Looking at things from that perspective, the 3.55 aftermarket gearset begins to look a lot more budget-friendly. Granted, us old geezers who aren't intimidated by setting up rear end gearing are getting a little scarce, but it's not impossible to do.
Jerry
