Whatever the two speed axle is the ratios are probably slow and slower. So, one needs to get a Brownie or such, and then upgrade the brakes, or get a modern rear axle with modern brakes.

For bigger trucks, 630 etc., higher ratio two or single speed rears are available, I got a 4.13/5.59 for my original 6.5 axle, however, one needs to find someone(rare) who knows what one is talking about.

Ed

Last edited by EdPruss; 08/01/2020 12:08 AM.
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.