motor
 

I have a 99 gt, just a quick question if I was replacing the motor i could put a 4.6 from any 99-04 gt in it with no modifications or anything right? Also what other vehicles and from what years could I take a 4.6 from to swap into my car?

Any 99-04 mustang GT engine will work.

99-04 crown victorias, 00-03 F150s also came with the same 4.6. You'll need to be careful about finding an F150 with a 4.6. Many come with 5.4's. If you have to replace the motor anyway you might consider a 5.4 swap. Buy the intake from hiperformancesolutions.com and 1 minor exhaust mod and it's otherwise a bolt in.

Any 4.6 w/ PI heads should fit fine. Keep in mind the cars and trucks have different intakes so if you pick one up from a truck, I'd grab a car intake.

I also agree with r3d. If you're going through the hassle, might as well upgrade. Either through more cubes and/or a performance rebuild

I am definitely wanting to get a new motor in my car asap, what years and vehicles should I be looking to get a 5.4 from (I know some of them have different heads than others)- im looking for the most simple swap possible. I have my complete 4.6 and actually have an extra intake laying around for a 4.6.
All I would need to do is buy those intake spacers and then re use the stock 4.6 intake and all of my accessories will bolt onto the 5.4 or I could even use the accessories that are on the 5.4? and then what needs to be done to the exhaust? do I need to have the computer re tuned or anything?

For the exhaust, the mid-pipe needs to be modified to accommodate the wider/taller engine. For accessories, you can go either way. The computer will need to be retuned (you're adding 49 ci after all). As for what years, look for a PI headed one.