BB to SB 727 interchangeability

Hey guys, I’m planning on finding a big block for my RamCharger in the coming months and am trying to figure out exactly how I want to do it.
It’s currently got an 81 318 and 4x4 727 that I just rebuilt in it. The transmission works flawlessly, but I’m not a fan of the 318 in this big truck. And please don’t try to convince me to stay with a small block, because I’m not going to.
If I found a late 70s motor home 440/727, I’m pretty sure the tail housing would fit, but would it be possible to take the 4x4 tail shaft, and possibly all of the guts out of my small block trans and swap them into the big block trans case?
My long term plan is to swap in an NV4500 or a TR4050 5 speed, so I don’t want to spend a bunch of money on a fancy BB 4x4 727 when I’m just going to remove it later on.
Thanks!