Two, probably 12 V batteries were in there, that is what is in my '54 630 with a 503. If a giant alternator, must change diodes on housing to use neg. ground system. Put in a 4.33 two speed, helps with the speed. Had to install a later model GMC water t'stat. Got juice brakes working, too. Removed 16' bed, shortened frame 4' , going to 8' bed.

If the brakes don't work, a .375 Allen wrench rotated in wheel direction will tighten them, however, the mechanism is zink, most likely, easily broken, so don't lean on the wrench too hard. Repair is difficult.

Changing to a 4-71 could be done, some cowling work, radiator shutters, air intake and filter, etc. Might be an overwhelming project. A Cummins 6-bt would fit right in there, but it wouldn't sound right.

Ed.

Last edited by EdPruss; 12/28/2018 9:17 PM.
'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.