I used the aluminum ones, Percy I think, on the collectors. I just used the ones that came with the headers for the connection at the head.
FYI, if you have cheap headers like me and my friends do and are having problems getting em to seal, try these tricks:
If the collector flange is not part of the collector, weld it to the collector. It prevents the flange from distorting and letting the gasket blow out. I've even been able to use the crappy paper gaskets that come with the headers with success after welding the flange on and having a reducer that is solid. The set of Hooker Pro-comp headers I had came with the flange welded but they were a little more $$$ than the summit specials I have on this truck.
If you can't get the gaskets to seal at the head, try cutting /forums/images/graemlins/hack.gif the flange so each tube is seperate. On a SBC, obviously the the 2 center tubes will be together but the front and rear tubes will be seperate. This allows each tube's flange to seal independently, which seems to work better. My buddy has a motor with Dart angle plug aluminum heads and he couldn't get em to seal at all and was blowing gaskets all the time. After we cut the flanges on his Hedman headers it sealed up nicely and it even made the bolts go in easier. Now he has no problems with the white Mr. Gasket header gaskets from Autozone.
Just a few tricks that worked for me and my friends. /forums/images/graemlins/thumb.gif