Spicer: source? I think you're thinking of the 5600, the slick as hell 6spd. I've only seen the 3500 in the AA catalog as a good little truck tranny, like 1/2t or smaller. To wit: Medium Duty 4x4 trans , p.28.

Here's some other bad info: 1st- 4:01, 2nd- 2.33, 3rd- 1.39, 4th- 1.00, 5th- .78, Rev.- 3.57 dry wt: 97lbs.
Recommended as a replacement for the POS Peugot 5spd that came in a lot of Jeeps.

The new 6spd looks good to me.