315/60-15 (30" tall) on 68 Firebird what do i need to do?

[Shawn MacAnanny]

I've decided that i definately want to go with 4.56 gears and that i would like to use a 30" tall M/T ET Street radial. My rims are (i think) 15x8 although I'm not entirely sure. They have 26"x10.5x15 MT slicks on them. I know these exact wheels fit my 94 Camaro with no clearence issues if that helps with determining back spacing. There is a picture in my signature with these wheels on the 68.

Now i would like to go to a 30" tall tire which i have found that Mickey thompson makes in an ET street radial. I do plan on driving this car quite often and here in DE rain storms come out of nowhere sometimes. Anyway i was wondering what would be required to run these tires with the factory 68 chasis. I think i would also need 15x10 or 15x12 rims wouldnt i? I used to run 315s in 17x11s on my 95 formula but with the added sidewall height i think i can get away with a smaller rim. The car does have adjustable shackles, multi leaf springs, SFCs, and lakewood tractions bars.