ok here we go, 91 rx-7 non-turbo with HKS Hi-Power Exhaust http://www.hksusa.com/products/?id=715&rsku=3836 then thinking of adding Catalytic Converter Replacement Pipe with Presilencer http://www.racingbeat.com/FRmazda2.htm would I then want a new header? if so who makes good ones?

after that what would you people suggest to do next?

Go with the rcing beat header and presilancer. Actually the presilancer was made for that header. It will be very loud I hope you know that.

ok so theres:
A.presilencer and cat replacment
B.presilencer and header

if I get A won't I need a new header still and if I get B won't I still need a new cat? and which way would be best for a N/A

Presilancer takes the place of the cat.

With the racing beat setup you need to replace the cat when you do the header. Their lengths are jacked compared to stock. I cannot remember the exact length diferences right now but I know we tried to use the RB Header on my bro's GXl and it would not work without using the presilancer.

I honestly would call Racing Beat and talk to them they know the best.