I have a 1990 LX 5.0L convertible. I am converting to 5 lug wheels. What modifications, if any, will I have to perform to get a set of 17" wheels from a 2002 GT to fit with 245/45ZR17 Tires to fit? Will I have to roll the fender lips under at all?
All of these new people!!! Welcome! This is a very common question. If you do a search on brake upgrades, you will find a lot of threads on the topic.
See Matt90GT's website - http://svo73mm.cjb.net for ALL your questions on 5 lug conversions and Fox brake upgrades.
But basically, you need to use the 94+ sn95 front brake & spindle setup if you want to run them correctly. That is what the guy above basically has, but with Cobra brakes. You can mount them on the SVO/ Mark VII rotors on your spindles, but you will not be able to install the center cap without some thick spacers, if at all. The proper way, to avoid any fitment problems, is to go with the SN95 setup. I have it and the 17x8 wheels and 255-40-17 tires fit just fine.
For the rear, either 5 lug drums, stock width disc, or the 94-98 SN95 disc setup will work fine. You might want to roll the rear lips if you go with wider tires, but you would probably be OK with the stock size tires.
Read Matt's site and let us know if you have any more specific questions!