Wheel spacers?

I am planning on leaving my car SBP and want Ralley wheels for it. This limits my choices. Today a friend told me they make SBP to LBP adaptors which add about 3/4" to the outboard offset. Has anyone here used these and if so does one need to buy deeper offset wheels to compensate for the added width. BTW, I am still in the market for a set of ralley wheels as the last deal fell through.
TIA, DM