My car had headers on it when I purchased it in '76 (which is probably true of 99.9% of early Z28s. I do have a set of very nice original exhaust manifolds that I will be installing (1st day take offs from a friend's TransAm car), but I didn't get the heat riser with them, so I'm trying to figure it out myself. From the discussion to date, we do not seem to have a consensus as yet. Personally I prefer the 'underneath' position that matches JOhnZ's car, the '68 magazine pix, and the AIM, assuming it doesn't interfere with anything, because that orientation seems to be a more 'neutral' position of the weight wrt gravity, and it's more out of the way.