mini tub pictures

When mini tubing do you have to shorten the rear axel?

No.
I run the stock 52 5/8 width housing (A body 8.75) with the wider axle flange. (B body)
It's the custom offset for the wheels that makes it hard. I have 15x10 rims with 7 1/4 or 7 1/2 inch offset. Cant recall off the top of my head.
Plus I run disc brakes with 1/4 inch thick rotors which moves wheels out.

I did my own custom wheel offset
Home made 15 x 10 with 5 on 4 1/2 b.c. and dog dish hubcaps.