Is the engine a Chevy or GMC? Chevy's are about 3" shorter than GMC's so if the fan is way short of the radiator, Chevy, if about .75" short of the radiator-GMC. GMC's SN, r side, stamped on pad by starter, start with displacement, I. e. 228xxxxx, etc.
'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.