Kris,
The cost to convert your truck to overdrive really depends on what you want as the final product and how deep your pockets are...You can get higher speeds by swapping out the existing 2-speed rear for one with higher gears. I did this in my fire truck for less than $500. Or you can search for a 5-speed OD transmission.
"Any particular differences between the 58/59 spartans?"
Not sure I understand your question..do you want to know from year to year or Apache to Spartan? There aren't any major changes from year to year (58/59), but from Apache to Spartan there are tons!
All TF Cabs share the same cab mounts...a BIG truck will work on a small chassis. About the only difference I know of is the transmission floor covers are cut larger on the big trucks, but that normally not a problem.
"Any idea how hard it would be to throw on an 80's GM 1-ton chassis (I kinda have an appreciation for disk brakes and power steering) - around here they aren't hard to find completely rusted out but still running and usually have descent drivetrains too"
I'm not the one to ask about swaping chassis, but I'm not sure you really need to swap. Unless your going to load this truck to the max, why do you need new disc brakes? This truck has MONSTER size drums and is designed to stop 25,000 pounds! The 1 ton modern chassis is only rated at about 12000 pounds...I'll put my big Hydrovac brakes against the 1-ton disc brakes any day. I don't have any trouble locking them up!
As for steering have you looked to see if the Spartan has Power Assist Steering from the factory? You may have more there to work with than what you first thought!
Drop in a Chevy motor of your choice, big or small. Change the rear gears for better speed. Shorten the chassis to fit your pickup bed and GO!
I like the Tonka Truck!
Send pictures of your Spartan!
Mike
