8000 series is HUGE
7000 series is to big for all practical purposes in an AD 1.5 or 2 ton.
6000 series is on the verge of being to big for an AD 1.5 or 2 ton, but would probably be OK.
5000 series (5831) would be ideal with stock engine.

I have some pictures of auxiliary transmissions of different sizes on my web shots account (link below).

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-