Stop PM'ing me on this if you wont actually take my advice.
1. you should not machine the Magnesium wheel , these things crack, break, alot easier than aluminum, they were made that thick for a reason.
2. the front fits fit pretty good as is, i put one on my boss's 98 we had here and i liked how it fit, it came right out to the hood line, so just put tires on and test fit them on the car. hypothetical measurements trying to get them to fit like oem wheels is not the best way, just test fit them to the car, alll the pictures of the other "comp coupe wheels" are all different wheels than the BBS you have. the oem gen2 wheels my boss's had on his gen2 gts that was lowered looked like they needed to be spaced out 1" to me, they looked sunken in and narrow. his car was on aldan low version coilovers.