Skip,
I consider only the late 47-53 and sometimes the 54 trucks as Advanced Design. Someone else may have more on this.
As for better gears for your truck.
You don't need a two speed, they are all really big and slow. With the exception of some rare and really old stuff that is probably not worth the money or effort.
You may want to look in to swapping a t-5 from an S-10 for the overdrive.
Start measuring vans you see in parking lots to see if the track with is the same or close to yours, then find a rear in a salvage yard for that van, it will probably have a 3.XX gear ratio if it is newer. I just sold a Dana 60 from an 80 something Ford 3/4 ton van. The axle flange to axle flange is 4" wider than a 52 Chevy 1 ton, perhaps exactly right for your truck??
Most any new axle can be easily adapted to disk brakes with a kit if you wish. Don't put disk on the rear unless you have them on the front.
Look into the Saturn overdrive that bolts on before your transmission, cost less than the gear vendors unit I think.
Taller tires help with the speed. My 52 1 ton fits some 8r19.5 tires that are 31" tall.
Decide how fast you want to go and at what engine RPM. Plug the numbers into this page and find what tire size, gear ratio, and overdrive ratio you need to do what you want. If you plan to work your truck don't gear it so fast that you can't start off with a load without burning the clutch.
http://www.4wheelparts.com/4wp/ORS/gear_calculator.asp There is a better one out there but I can't find it right now.
Grigg
