Do a compression test on each cylinder and apply air pressure to each cylinder. If compression test is about normal on each cylinder and you get bubbles on a certain cylinder when you apply pressure you more than likely have a cracked head. You didn't say what year 350 it is. If it is an orange engine made in the 70's or before the heads usually stood up pretty good but the newer heads are lighter and have a history of cracking.
If 2 cylinders show a distinct presure drop you may have lucked out and blew a gasket.
Heads still not to big a problem. 350 heads (or whole engines for that matter) are pretty cheap and easy to get ahold of.
