Backspacing Help Needed - 67 Camaro - Specs Listed

[bigboi]

I need some help and advice from you guys...

Here is my scenario...

I have a 67 Camaro running stock suspension w/ drum brakes on all four corners. My plans are to install disc brakes in the near future and lower the car to sit right above the tires after I install the new wheels/tires.

You can see pictures of my car at www.biigboii.com.

Here are my measurements...

Rear:
Drum brake mounting surface to inner wheel well - 5.75"
Drum brake mounting surface to fender lip - 5.25"
Total distance from wheel well to fender lip - 11"

Front:
Drum brake mounting surface to first obstruction - 5"
Note: This obstruction is very close to the backside of the drum brake.

Here is what I want to run...

Rear:
18x9.5 Billet Rally
275/40/18 BFG g-Force T/A KDW
Section Width on 9.5 wheel - 10.9"
Overall Diameter - 26.7"

Front:
18x8 Billet Rally
245/40/18 BFG g-Force T/A KDW
Section Width on 8.5 wheel - 9.6"
Overall Diameter - 25.7"

Backspacing Help...

Rear:
Since my mouting surface to wheel well is 5.75" what backspacing should I go with? 5" or 5.25"? 5" would be safer, but can I get away with 5.25"?

Front:
I have been told to go with a 4.75" BS from another board member. The front is a little harder for me to determine because it doesn't seem as "cut and dry" as measuring the rear. Can any other Camaro owners help me with this?

Thanks Guys!!