I ended up buying a set of used Alcoa 9K 9.00's from a garbage truck. They were fairly rough but easy to polish back to life and $80 each. Even though it was some work to get them back & looking good I knew the Alcoa's would be a good wheel. Mine are the standard back spacing and I did loose a little steering radius. As you're probably running into, you can get different back spacings that will push the wheel and tire out a little further. I just decided to deal with the standard wheel and it's been fine so far.
Also BTW, Michelin has some great information on their tires & ratings in their Data Book. Page 75 gives the load capability vs PSI of the 315. Somewhere in there they also denote the de-rating of the 315 if it's mounted on the 8.25" wheel.
http://util.michelintruck.com/databook/DataBook.pdf
http://www.michelintruck.com/referen...nd-warranties/