Got the machine, which has a Digipulse feeder with a plain aluminum "mystery box" attached. Stan Smith suggested it's an interface box for a push-pull gun (which I didn't get with it) and tech data confirms that.
Turns out ESAB 450i cvcc do pulse, but require pulse accessories to do it. They do 275A single-phase or 450A three-phase. Runs fine off a 50A breaker though I haven't maxed it out yet.
It stick welds nicely (I need one more cable to run the feeder) but requires an external control be plugged in. They won't strike an arc without the correct external accessories, but they will power up. Keep that in mind when inspecting used machines.
I find it quite annoying, since I want to do straight stick at a distance without a remote, but I'll settle for leaving a brick on the TIG pedal. It would be easy to make a dummy TIG control circuit and plug it into the connector, and I likely will.
These machines have been around a long time, and are originally an L-tec product. Internal inspection reveals they are very well made. I'd buy another. I'm sure the reason I got it cheap is low public awareness. Fine by me!
ESAB could make things MUCH easier for their customers by better indexing their download library and using INFORMATIVE file names. A few days work at most for one person. They could also support a user forum, but all they have is a (lame) Facebook page.
Miller and Hobart have by far the most useful corporate-sponsored forums, so they win by exposing potential customers to their offerings.