there is a big performance diference. like for your example of the 440, fyi they stopped making tthe 440 in 77, the compression ratio was dropped big time. in 68 it was 10:1 and in 74 it was 8.2:1.also you have to think about the emissions systems that were starting to be installed. another fyi in the late 70's you could only get the 440 in trucks and some cop cars. so if you think of the difference between a 69 350 and a 82 350 it is just as bad if not worse. you also have to think about the machining differences like the heads, the valve sizes, the cam size there is alot that is different between the years. to help you further here is a page with the 440 info.
http://www.lhmopars.com/engines.htm since your trying to buy an engine a couple of questions have to be asked. is it going to be a crate engine or out of anthor vehicle? if out of a vehilce are you going to rebuild or just throw in? if your rebuilding it the year of the engine matters to the point of cappabilites of the year block and heads. if its crate you can are you getting a long or short block? i could keep going but i think i answered your question already.