welp as for putting it down on 18s you should be able to get away with not having to cut the inner fenders completely out ( dont quote me on that though cause i never had mine on 18s ) but you will need to redo that tranny x-member to completely frame it
but got with a F/S upper cup in the front w/ 2600 (or a 2500 whatever your preference is, i went with a 26 and like it )
and just be carefull of shit like heat getting the lines all that cause the headers are fairly close to that upper spring pocket
and it seems i was the only one but i did have alot of balljoint problems and ended up needing to take care of that with tubulars but i dont know bout on 18s, you should be fine, just somethin to watch out for
any other probs just shoot me a email and i'll do what i can to help
jimmy@centerstagecustoms.com