I think the vortec heads are a great bolt on head for any older stock 350.
You might want to go to Amazon.com and look for some books on small blocks. There is an interchange book and one for casting numbers. This way you can look at the numbers that you find an know what you are buying. I have these books and find them informative. Here is a search that brought up these books.
http://www.amazon.com/gp/search/ref=br_ss_hs/103-1100170-6642258?platform=gurupa&url=index%3Dblended&keywords=small+block+chevrolet+casting+numbers
