If it was mine, and I have a 250, I would add the 307 pistons for the compression increase, look for a slightly bigger camshaft, have the head rebuilt as it is, clean up the head to block surface, and add HEI ignition. It will sound better with higher compression and run better. You go adding a lot bigger cam will wreck the idle quality. The Lump port inserts work if you spin the engine to higher rpms, they actually work really good, but for a normal old truck, you probably won't notice the performance increase. Dollar for HP gains will be the compression increase, keep the manifolds you have. Be sure to add water heating to the intake if you don't have it already.
