D100 Pickup question for you:

They DID make a later model higher-first-gear model of those "truck" transmissions, maybe you could swap one of them in. It would keep the "truck" appearance and give you a "more useable" first gear.

Read this:

The Novak Guide to the New Process 435 Transmission

1st 2nd 3rd 4th (direct) Rev.
NP435A (Dodge, GM) 4.56 2.28 1.31 1.00 5.64
NP435L (Ford, Dodge, GM) 6.68 3.34 1.66 1.0 8.26
NP435D (GM) 4.90 2.29 1.19 1.00 6.06
NP435E (Ford) 6.68 3.34 1.74 1.00 8.26

Or you could swap in a later model A833 overdrive 4 speed, which was used in some later model trucks. Of course you need to be sure the /6 has enough oomph to pull whatever rear gear is in the thing.