What you are paying for is fit between the flange and head and what coating you get. The fit of the flange to the head is pretty obvious. The better the fit the less leaks=more power and the less work to install. The other main thing which is very expensive is the coating on the header. The ceramic or Jet coating option is definately the way to go for longevity. The heat from the headers will bake off the paint pretty quick exposing the bare metal to the elements. Your headers will look pretty nasty in a very short time and probably will need to be replaced in a few years. Please forgive me but I am assuming that you are looking at long tube headers. If not please consider them because they will give you more power. Another option that I forgot to mention above is the primary and collector size. The larger primarys will give you more high end power and the smaller ones will give you more torque as a general rule... Choose according to what you are trying to do with your engine. For a small block, low end torque is a good thing. Collector size is how big of an exhaust you are going to run. 2 1/2 inch is pretty good for a small block. There probably wont be much of an HP gain but you might loose some torque if you go with the 3 inch. I suggest looking at Hooker Super Comps w/ceramic coating and BBK long tubes w/jet coating. They are expensive but you really get what you pay for. Hope that helps.
Kevin
