The oil pump on a 304 is external. It's at the bottom end of the timing cover. There are gear-to-housing specs. If yours are within spec, they don't need to be changed.
If you do decide to take measurements, and check it out, you'll have to prime the pump...fill it with Vaseline, before starting the motor.
'79 CJ5, AMC 360, t-18/d20 twin stick, dana 30/amc20(Mosers), Edelbrock Performer intake, Holley 600, ps/pb, DUI HEI, 'glass tub/1pc. tilt nose, 33x12.50 BFG AT's.
There's a fine line between "hobby" and "mental illness".