Ken's Classic muffler company in Longmont. 251 Collyer St. 303-772-6171. Just east of Main St(Hwy 287). Make an appointment, they're always busy.
These guys are REAL pros, they do custom bending and build performance exhausts on just about anything, they're also a Flowmaster dealer.
They did a complete 3" system from the headers back on my '96 F-250 460. Fair price and some of the most beautiful welding I've ever seen.
I would go to Ken's in Longmont, I've heard alot of good stuff about them. Boulder muffler really stuck it to one of my friends a couple years ago,that's all I'm gonna say on that. The Mieneke up in Greeley does good work too. They put a system on my '58 for a pretty resonable price, and did good work too. Just my 2cents.
His an example of the Mieneke in Greeley's work. Check it out, they built the headers and did all the other work. It's 2 or 3 pictures in.http://home.att.net/~ambroberts/Frankenstang/ Sorry I don't have any pix of my '58.