I am wanting to put 5.0 In my 98GT. But I don't know a whole bunch about newer cars and all of the computer what not. What all do I have to do to make it happen? Somebody please point me in the right direction.

Well physically it'll bolt right in if you get a crossmember from a '94 or '95 that had the 5.0 engine.  Then get a computer and harness from a '89-'93 and you shouldn't have any problems.   

Thank you for your help. that is exactly what I needed to know.

Anytime, just make sure the computer's from an '89-'93 and not the '94-'95.  They don't like any mods to be done and you'll have a serious headache with it.   

Ok I have another quick question for you. Will I have to make any mods. to put the crossmember from the '94,'95 into my car. Also say if I couldn't find a '94, or '95 junker around here to get the crossmember from. could I use an aftermarket tubular like one that I saw in Summit racing part # GRN-GMTK7995. Sorry to bother you I am just a young kid trying to tackle my biggest project yet.

Naw, you're not bothering me dude.  If you get the K member, make sure to find out if you need the control arms with it or not because with some members the factory arms won't work with it and you have to buy more parts to make it work.  It'd be worth it but more expensive.  If you wanted the factory member, you could call places like MPS or Dave's Mustang Parts and they should have it.  So you can go factory style and cheaper or aftermarket but more expensive.   

I am glad that if found this topic because i am looking to do the same with mine, I have a 98 GT with a few modifications, Magnaflow offroad x-pipe, bbk cold air intake, flowmasters, cut the cats out, and a superchip, did all the mods @ 70,000 miles and now @ 124,000 miles the motor is acting up very bad and i dont know what it is, i have to get it in 4th gear just to get to 60 mph. I was gonna swap to a 5.0 carb. but people told me that it cant be done in a 98 without forking out 10-15K. I guess from reading the following info it seem like it would cost as much as i heard it will be just a little labor involved?