The 15x7 88 rear wheels are essentially the same casting as the earlier 15x7 wheels, except that they are painted different colors, and the valve stem is drilled in a different place. I have measured the offsets of both wheels. They are identical in that regard.
The 15x6 88 front wheel is essentially the same wheel, minus the 1" lip on the front face.
I have seen a set of 88 wheels mounted on an earlier car. They fit fine. The fronts look a little bit "tucked in" under the front, compared to the regular wheels, but there were no interference issues at all. The real advantage to using those wheels is that the steering should be a good bit lighter, due to the decreased scrub radius.
Raydar88 Formula IMSA Fastback. 4.9, NVG T550 Praise the Lowered!
[This message has been edited by Raydar (edited 07-11-2015).]