This has been discussed all over this forum. The 10" wheels will cause for the tire to rub on the inside fender well somewhere (I believe it was the frame). I am not that familiar with the 1st gens, but I'm pretty sure you will run into a problem with a 12.50 on a 10" wheel without a lift. Also, a tire place WILL NOT mount a 12.50 on a 7 inch wheel. I don't even think they will mount a 10.50 on a 7" wheel. Just do a search and you'll find tons of information on the 1st gens and the 10" wheel problem/issues. Just repeating what I've heard people run into with a 10" wheel.
-Drew