TH375 to TH400, swap tail shafts?

[zieg85]

First of all I am not a fan of automatics as I know zero about them for the most part.  I know of a good TH375 that my friend ran in his 68 Camaro behind a pretty stout 427.  He went to a 700R4.  From what I've read the TH375 is a TH400 with a TH350 tail shaft slip yoke.  I still need to confirm that but seeking advice as what the difficulty level into swapping out the tail section with my ailing TH400 (fixed yoke with 2 piece drive shaft) in my truck.  I haven't been inside an automatic other than a filter/fluid change which don't count.  Any insight, I am all ears or should I say eyes...

[Captkaos]

That is essentially what it was, but I believe it had less clutch packs also.