Late '90's with a clean or salvage title would be outstanding! I don't think there's any difference between any of the frames for the air-cooled bikes up to the S*R years. PM or e-mail me. Pleeeeease. 8)
I think the four-valvers have a wider frame to accomodate the wider engine, but I could be wrong. Do you know if this is the case? For some reason I remember reading that the S4 frame came from the ST4 and is a bit different from the frames for the air-coolers. ???