A good question and it can be done.
I updated the three speed I had in my 37 truck with 54 transmission guts. Everything worked fine and it did make for a better transmission. I soon tired, however, of not being able to move well in traffic, always having to down shift to second and having to come to a complete stop to shift into first gear.
The real deal is to find a mid to late 80's T-5 five speed transmission commonly found in the S-10 Blazer. With an adapter from Buffalo Enterprises and an open drive line, you can have a syncronized first gear, and overdrive gear to keep up with traffic, the other benefits of a T-5 transmission. You will have to convert to an "open drive" line, but it is not that hard to do and there are quite a few different rear ends that will bolt under your truck from a 55 Chevy (Powerglide) car to an S-10 rear axle.
My truck has a 55 Chevrolet car Powerglide rear axle, a 3.54:1 gear, and a 1985-1986 T-5 transmission along with 54 Chevrolet car front spindles, hubs and brakes and it is a joy. I can put virtually an wheel I want on the truck and I'm not restricted to a 6 lug wheel, I have Bendix brakes on all four wheels, it stops on a dime and I can cruise at 70 mph all day long with a tach reading of 2200 RPM's.
I think you're thinking right!
