Jegs, Pop Hot Rod mag, list/talk about them. Web site is www.pertronix.com.

Their BBC Tri-5 caught my eye. Few headers are available, and most versions out there are big tube, poor clearance, etc. These are 1-7/8" x 3", boast good clearance in engine compartment and to ground, available raw or coated. Should be an improvement over the '66-Impala-chassis-w/#5-tube-smashed-for-steering-gear-clearance version I'm running now.

The "Pertronix" part makes me wonder, though. How does their ignition experience translate to exhaust? Does the fact that my '57 got consistent after removing their points-conversion set-up and installing the GMPP HEI have anything to do with my concern?

Any thoughts/experiences?

I understand your dilemma. I often shy away from "new" products from a manufacturer not seemingly experienced in that area. If you have a magazine testimonial to refer to, that may be somewhat encouraging, but I often wonder if the writer may have his own agenda for printing that opinion. (Favors? Profit?)
Regarding your Pertronix experience, that wouldn't be a big confidence builder for me.
All in all, it's a leap of faith. I, for example hope my SLP headers fit better than some people report. Should know before too long...
Good Luck.

The mag reference wasn't a write-up, it was a "new products" feature - all the more reason for caution...

The ceramic coated versions are about the same price as Danchuck's chrome plated offerings.