HELP!! Big problems with 99 Grand AM

I have a 99 Pontiac Grand AM with 84,000 miles on it and we think the engine is destroyed. It started out just acting like it was bogging down on my way home from work one day, no real power. then when my dad took it into his body shop to look it over it started nocking loudly and makeing a loud winding noise every once in a while. It does run, and sometimes it sounds fine, but it is currently parked in our drive because we have been told by 2 different mech shops in the area that it needs a new engine. they think it has something to do with an intake or header
gasket problem(to indepth for me to understand). so 3 weeks ago we started the hunt for an engine. What a chore. We have found a few but most are either high mileage or an outrageous price. My dad still seams to think the engine may be fixable. Any idea's would be greatly appreciated, and is it true that these engines are starting to get a reputation for seizing at around 80,000 miles?

thanks

throughing any codes? and can you explain the nosie it makes a little more.

You mean warning lights right? If so, no not at all. thats another thing that really baffled me about it. not a single warning light. I think the best way I could explain the noise would have to be..... after lightly reving the engine when the rpms were comeing back down it would pick up a winding type noise that was loud at first and got quieter as the rpms came down but didnt always go away completed until after it idled for a little bit. It didnt do this every time we reved the engine but I think it actually will have a quieter winding noise every once in while when it just idles too.

sounds like air whistling a bit? when you rev fast does it make a hi pitch pishhhh noise?

is there any water or coolant in your oil?

no coolant or water in the oil. my dad sais it didnt really sound like that. he sais it was rapping. i thought it sounded worse than just rapping but i guess maby its just a louder worse form of what i have heard before. my car would always make a very slight rapping noise when i first started it up, but it always went away after it warmed up a little bit.
we picked up an engine today that, according to the guy who sold it to us, came out of a 99 grand am with 32k. now we dont think its the right year. my dad noticed that the one we picked up has emission tubes on the front and mine doesnt. he thinks its probably older than mine and from what we've been told only an engine out of a 99 will fit in my car. aaaaaaaaah! this is soo frustrateing. it has been 6 weeks since we parked my car in the drive, and try to figure out what to do.