51 phatboy, what i would do is pull trans cross member out support rear of trans with jack, measure front of engine center of vibration damper to frame rails with engine bolted down on engine mounts, measure rear of tail shaft center to frame rails to make sure it is centered, after engine trans is centered in frame, put level on carb top or intake manifold jack up or down rear of tail shaft until level is level, this will tell ya where trans mount should be , adjust motor mount, trans mounts to align engine trans square in frame, also check rear axle, drive shaft alignment so it is straight from front to rear, also check degree of rear axle to trans drive shaft fit, you may have to modify trans mount or buy hot rod trans mount to get good fit,
Hope this helps, also mit check engine trans swaps
hot rod web pages, I believe most trans mounts on frame vehicle bolt to the top and bottom rail of frame and are adjustible to some extent mit try measure frame rails check salvage yards for suitable donor trans mount that will fit better than what you have. maybe someone else will jump in with better Idea. good luck
jbennett
40 burb
