1 guy on ntba facebook site bought a set , said they appeared well made , he hasn't fired the car yet. I've been looking at them , they don't offer a collecter/muffler/extension. One saye 3.375 od collecter , one 3.4". I don't know if the 3.5" speedway extensions would work. If you had to have something custom made , that could get expensive. From what I've been able to gather ,they turn straw yellow w/heat , but can be buffed out. Hell of a deal if you can find an extension/muffler to fit. They are 16 ga. , tig welded & a 3/8" flange.
dave