Hello
Hell those 996 standard seats are not worth to be fitet in a Porsche.
OK they are nice and lighter then the "real" units but made by the Lear Corporation ( wich bought Recaro ) and have the same quality like mexican made Recaros. Even BMW now has better seats
You can fabricate someting that will fit them on the old rails.
@Mik
The 964/993 seats will be a direct fit for 86 on 911 ( big dash vents, wide demisteropening on windscreen, Hazard & Defogger switches in centerconsole ) )
Grüsse