I have just been through this question with the backspacing. I have ordered wheels that are off the shelf and am awaiting shipment although I did receive one rear wheel and test fit it with an appropriately sized tire.
The below information is my best approximations based on available data and should be verified but it is a starting point.
Wheel Data
Narrow Body Hub width 61.5mm
Front OD 25"
16 or 17 x 8 backspacing 4.75in Offset 20mm 225/40R17
17 x 9 backspacing 5.25in Offset 20mm 245/40R17
Rear OD 26.5"
17 x 11 backspacing 6.0in Offset 13mm 335/35R17
18 x 10.5 6.0in Offset 19mm 295/35R18
18 x 10 6.0in Offset 25mm 275/40R18
Enkei RPF1 center bore 73mm
16 x 8 offset 15 225/50R16 OD 24.9 sect width 7.3
17 x 10 offset 18 285/40R17 OD 26.1 Sect width 11.3 (this fit great with just enough breathing room - didn't stick out to edge of fender entirely which was my goal)
These last wheels are what I am going with - $1100 for the set, I'll post pics when I have them
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