easy way to figure cam lift on sbc in truck? worried changing heads

[knightowl73]

all i know about the motor is that its a 350 4-bolt main and it has a unknown erson cam in it. its a nice lumpity cam i know that much, makes the raggedy truck have such a cool factor as long as its running.

im switching heads this weekend on it, it has stock 350 heads on it, my buddy just upgraded heads and gave me a set of 305 heads that he had bigger valves and port n polish done to.

im replacing the lifters for the hell of it, i think they are toast and need replacing anyways since it gives lifter noise when i "launch" it too hard, but i run the *#@! outta this truck already, and this should hopefully be a real nice upgrade.

besides the higher octane fuel, what else should i be concerned about? will i need to know what cam i have, at least lift,pushrod guideplates or anything lke that? the new heads come from a motor that only had a rv cam in it, and it had almost as much nuts as this truck now. will i have to play with the timing because of the higher CR or can i just mark the distrib and stab it back in with no issues?