Thank you, Ken, for starting the thread – it really forces us to look back at the record and see what was actually built. Not to mention comparing that to our often sketchy memories.
The commercial racetrack field is especially nebulous in fact, since there were so many different companies doing it, from fly by night to major, and they didn't always leave much of a trace... Not to mention they were region specific in many cases. American Model Raceways is generally considered the biggest of the bunch, and the most widespread, but of the five or six raceways I visited in my youth in Chicago, only one had AMR tracks. And the hobby shop I worked in on the south side of Chicago when I was 16 had an eight-lane high-banked Formica track, and I have no idea at all what company built it!
A lot of shop owners built their own, too. My local hobby shop first had a four-lane Strombecker track before making the plunge into the big one, and that may have been pretty typical, too.
For the moment, haven't found any trace of a Strombecker six-lane track for 1/32 cars – are you sure it was Strombecker? Of course, in '65-66 things were changing so fast that a new model may well not have made it into the company brochure, like the one I partially scanned above. I do vaguely remember a six-lane track or two, but haven't found them in print yet.
I would guess there were at least five or six of the commercial style home tracks like the ones shown above; I can think of three or four of these offhand, and I know that I've seen others.