I was thinking of trying them, but instead chose Waldrons Exhaust for my 71 Roadrunner. Showed up just before winter, so its not installed. Quality looks great, mufflers, etc. I chose 2.5" all the way and it was around 550 or 600 shipped to nearest Fastenall.

I had former coworker has used them many times with no problems. I think he also helped engineer the mechanical mufflers Waldrons sells (repo's of he rare GM units).

http://waldronexhaust.com