Couple 440 Motorhome and 318 questions

I'm not sure but I believe you could remove all the brake drum stuff and have a drive shaft made with slip yoke as some of the early Dart guys have done on flange drive shafts.

You could also look around and find a core with the standard long shaft, and it might be that if the 318 trans is a 727, you could use that shaft and tail housing

The bell housings are different between SB and BB so no, the 318 trans will not fit.

You'll need pass car engine brackets / mounts for your body, IE BB in that body, and a car pan and pickup. You may need different exhaust manifods