Backspacing for 315/30/18 ?

[dbs1]

I've got some leftover tires from my 67- Nitto NT01's. 2-275/40/17 & 2-315-30-18 for the rear. I'm looking for some lighter weight wheels to use for the road course with these and I'm assuming a stock setup would work with the fronts, but I am not sure what back spacing/rim width would be needed to use the 315's on the rear, or any other issues I might run into? The 315's are a good 11.5 wide, but are very close to the same height as the 275's, so no abs issues. Ideas/comments? 02 ss

While I'm asking-what is the least expensive brake upgrades for the front that will get this car to STOP?

[Eugenio_SS]

I'm using those in the front and rear.
I'm using C6 18x10.5 (+56 or +57mm offset; can't remember now)
All I needed was a 1/4" spacer and it's perfect.
Pix in signature.