73 tilt cab new project

[73 GMC 4 Me]

Hello all enthuiasts,
I have a 1973 6000 v-eight that I might want to make my toy hauler.
It currently has a 327 cid,4 speed and split rear.
I also have a running 91 1ton Chevy van I'm thinking of using everything out of.
Tbi 350, 4l80e and seats for now.
My first of many questions are
1. Is the 327 a standard engine or are they modified for these trucks.

2. Are the trans and diff standard for these (i.e.) sm420,eaton

3. Would the 350 and 4l80e be a good swap for mileage and a little more power.
Not a freeway flyer.
It runs so I have all wiring harnesses

4. Will the split rear work with an automatic (i.e.) run in low with load or high empty.

I will be very appreciative of any help or suggestions.
I have also noticed there's not a lot of the tilt cabs being resto'd