318 auto 727 trans hooked to the 4x unit. My question will a big block trans work by changing the guts of the 318 trans? I want to change over the drive train to my Lil Red with a 440. I know I’ll need a back driveshaft since the RC has a 6” shorter wheel base. Any thoughts?

You just need to change the output shaft and extension housing.

in other words, use the above on the big block transmission.
i did this on a 440 swap back in the late 70's on my 318 engine'd 72 w100.

Great, thanks, didn’t think it would take much to change over. One other question, is there a device to bolt on to unlock the front hubs like what I had on my CJ5 back in the day. Just so the front rear doesn’t turn all the time.

There used to be a kit to convert the np203 full time 4wd transfer case to part time.
You'll have to change everything from the knuckles out, to add lockouts.

There was, long ago, a kit to convert the small lug pattern full time axles to lockouts.

You'll have a better chance of winning the lottery.

IF you already have the larger lug pattern, then yes you can add lockouts, use parts from 85 to 93 plus the hubs, or 80 to 84.

Or plans on a rear axle swap and matching wheels.

Fwiw, keep the existing 203 case and full-time 4wd. You don't save enough to make a conversion worthwhile.

You also need to do something with the transfer case as the 203 case needs both axles engaged to work. You could swap to a 205 case but the adapter housing is different. After that you could also use everything off a mid 80's Chevy on the front axle housing, knuckles, spindles, stub shafts, hubs, rotors and brakes. The up side to that is you can still buy hubs for the Chevy stuff, the Dodge stuff not so much.

Sounds complicated, I’ll keep it the way it is. Not like it’ll be a long distance truck, just for shows.

Even if it was a long distance truck, converting to part time is a waste of time and money.

Good, one thing less to do

I can attest to this. I spent over $2K installing the free spin hubs on my '06 2500 Cummins quad cab, didn't even get a 0.8 MPG increase.