If the 235 is just rebuilt, stay with it for a while, when looking for more power, a 261 will bolt right in; GMC mounted the radiator in front of the radiator support vs. Chevy mounted to the rear, therefore if going w/ 270 or 302, must move radiator, watch for grille clearance or look for GMC front tin.

Various comments here about front disc brakes, etc., on your front axle.

Last edited by EdPruss; 10/05/2012 11:54 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.