W/Z manifolds are big block only. If you don't go with headers, you really only have 2 choices; 1) Use stock manifolds with a block-off plate on the crossover ( Olds did this from the factory on dual exhaust cars back in the day of true duals ), or 2) Get a set of the 'high performance' exhaust manifolds from Thornton. I had the Thorntons for a while. They were ported to be the best they could possibly be, but I noticed no gain vs my stock 307 manifolds on the butt dyno or the track ( though dyno claimed some gain... ). Overall, the Thortons are not a good investment IMO.
My recomendation is to save up a few extra bucks and get the American Racing headers now otherwise this will be a likely senario; You go with manifolds but eventually want more power, so you'll end up buying cheap headers and have to mess around with all the BS that cheap headers have plus spend more money modding the exhaust by switching from manifolds to headers. You'll then wish you didn't have to deal with all that header BS and finally end up thinking 'man I wish I would've just bought those AR headers in the first place and saved me alot of time, aggrivation, and money'.
My recomendation is to save up a few extra bucks and get the American Racing headers now otherwise this will be a likely senario; You go with manifolds but eventually want more power, so you'll end up buying cheap headers and have to mess around with all the BS that cheap headers have plus spend more money modding the exhaust by switching from manifolds to headers. You'll then wish you didn't have to deal with all that header BS and finally end up thinking 'man I wish I would've just bought those AR headers in the first place and saved me alot of time, aggrivation, and money'.
