1971 C10 402 with AC and g50 rear restoration

[RideLowInAGTO]

Half way through restoring this original black on black, factory AC with a big block truck. Currently the body is in the shop. New floors are in and cab corners. Fenders and doors are painted already. Just started body work on the bed. I also have the full set of trim for the truck. Engine is rebuilt and waiting on an engine stand. The chassis is at my shop where I've stripped it down to the metal for a new coat of POR 15 that I'm going to thin out. I have all new suspension for it front and rear including shocks and springs. Brakes are rebuilt front and rear.

I do have a few questions regarding a couple issues that have popped up along the way. So when I bought it, it had a 350/350 combo in it but it was originally 402/400. So I'm having trouble figuring out if I need the slip on yoke th400 or the bolt on? Also wondering what the correct length of tail shaft I need is?