Mine is a 55 2nd series.I am running a 350 Chevy engine,700R4 tranny,and stock 3:90 rear.It is one sweet ride.The 350 and 700R4 will fit in just about anything including your 50.As far as rearends go you will have to change it out if it has the stock rear in it,due to the closed driveshaft setup.There are many aftermarket motor mounts,trans.mounts ,etc.for these swaps.I dont know what rears will fit up to your 50,for tire clearance,etc.A couple guys around here are running Ford 9 inch rears in their ADs.If you use the 700R4 which is an overdrive tranny,you can run 3:90s,or even 4;11s.If you go with a 350 or 400 turbo,I would think 3:42s,or 3:08s would be a good ratio.
