wheel and tire combo help

[sprayed99]

I'm going to be using the Ridetech Street grip system, which Ridetech can't tell me what the complete amount of drop is going to be. So this leads me to my question. For anyone running a Ridetech Street Grip system or a drop near 4/6 I need your help. I'm wanting to run a 20x8 or 20x8.5 in front and a 20x10 rear. Tires will be 245 or 255 40 series fronts and 295/40 rears.

I need to know what back spacing your running and pictures would be awesome.

Thanks for your help!