need to see some pict.

[Mustang Matt]

I believe a factory 15 inch from a first generation Mustang had 4 to 4.5 inch backspace.

I have a set of the 05s (S-197s) on my SVO- they have a six inch backspace.

The earlier 94-04 (SN-95) cars had a 5.5 or 5.75 inch backspace- they are the ones pictured on both of the earlier cars- you can tell from the outer lip which is more pronounced on the early ones. The lip was reduced in 05 to fit the wider chassis of the S197 car.

You should need a longer spacer than that to run the S197 wheels. I would trade them for a set of SN-95s to both gain a more agressive lip and make fitment easier.

From the cars I have seen with spacers at 1' I would say that there is a lot more room to push them outwards before you hit the original wheels profile BUT you will have to content with rubbing in turns on the front valance if you go out too far- so it is a delicate balance.