[D13]

There are only a few differences in that era of 250’s. HEI vs points distributor, large vs small cap HEI, remote or integral coil, and some wiring.
Big change was head and emissions.

Looking at the driver’s side, is the intake clamped to the head or cast as part of the head?
If clamped then order your parts for a 1974.
If it is part of the head casting it is the “integral head”. Then the question is 1 barrel carb or 2barrel. If 1 barrel order parts for 1977 truck. If 2 barrel order parts for 1981.
Cars went to the integral manifold head first. Cars never got the 2 barrel carb.


Belts etc, best bet is to take with and measure.