Whatever you do, fix those bolt holes by tapping them next size so don't have to take pan off. A 302 GMC will bolt right in there(looks same on outside) and give significantly more power. Serial number, right side, behind starter, stamped, starts with displacement, i e 248xxxx, 302xxxx.

302's appear in larger trucks, not usually 1.5 ton, unless one has been swapped in, so look in all GMC trucks, just in case. Lots of military trucks, too.

Ed

'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.