If this were mine, I'd try re-torquing the heads as Garry mentioned, then changing the oil and use water as coolant for testing. Then I'd see how it works. But it might be a good idea to actually drive the truck, rather than just start it. I've had occasions where I've started vehicles and let them run, only to come back and find out that they had overheated. Luckily, no damage done...but scary.
Btw, head gaskets aren't wear items. They should last for a long time. But if you do have a major problem, now would be a good time to ditch that 305 and go with a nice 350 or 400 smallblock.
(You may have guessed that I'm not much of a 305 fan.)
