If you're wanting to sell it as a collector car in the future, get the PHS docs. People get burned and everyone seems to have the Trans Am used in Smokey & the Bandit - those cars are on craigslist every month!
There were apparently 3760 Y82 SE's in 77, 2856 Y82 SE's in 78 and 68 Y84's in 78. Those were the numbers on the 400/automatics. Not sure what 78's had fisher t-tops, perhaps the Y84?
So, the numbers, are they that important ...or real, probably not. The important thing is that you enjoy whatever you get. Drive it, get out to shows, have fun with it.
Post some pix of what you're considering and you'll get comments. Tell the seller to wait until you run it by some friends ...afterall, it's a buyer's market right now.