i wish i knew what your motor was as far as being a windsor or romeo, but here are a couple differences between the two:
1. if you are using windsor heads on a romeo block you need to make sure you get 8 new timing cover bolts due to the bolt size on the windsor heads are slightly larger & vise versa if you are putting romeo heads on a windsor block.
2. Romeo cam gears are bolt on and windsors are press on. (get the bolt on!)
3. Romeos run cam girdles where windsors run individual cam caps.
4. Romeo heads were made with a couple more spark plug hole threads so i would recommend running romeos to prevent spark plug blow out due to the bump in compression from the smaller combustion chamber on the PI heads. (though you really shouldnt have any problems with windsors just advise to be on the safe side)
5. Windsor heads are a 13/14 valve cover bolt pattern where as romeos are a 11/12 bolt pattern and depending on whether you run windsor or romeo you will have to find the right valve cover bolts due to windsors running a built on washer to fit the gasket and the romeos run grommets.
My advice is to try and find a set of PI heads that match your block so that you dont have to go on a wild goose chase trying to find bolts for the change in set up as i had to do. Saves a lot of hassle and a lot of money since you wont have to find valve covers as well. And to answer the question about the years theres really no differences between them. Hope this gives you a better idea. Good luck with the swap!
I forgot to mention i have a set of windsor valve covers with brand new gaskets if you are interested, they are painted gunmetal and come with bolts. haha