Your truck should have a 250 or a 292. Quickest way to tell which is distributor location and side cover height. The 292 dist. is front of center, 250's and smaller its centered. 292 is a taller engine, so the side cover is visibly wider.
The 292 will respond well to triple carbs and a mild cam and header, and look deadly too,'specially when you show it to some V8 guy that you just blew away at the traffic light! Don't try for the long run, though. They'll get you after a while. Gear her low and stick to the 1/8 mile.