It seems that Singers were like GM cars--they stayed the same for a very long time. I guessed that most of the black Singers and many early colored models had the same basic shape and castings, whether external motor or treadle. There are always bolt-on-motor-types sitting on thrift store shelves.
I made a trip to our local thrift store, which never lets me down. They had one labelled “Fleetwood”, but it didn’t ZZ. I was about to give up when I remembered one in a ratty case that they’d had forever, sitting on the floor in a remote corner. When I opened the case, a roach went scurrying for cover. The machine looked rough, but it was the kind I needed.
It was a Singer 306W. I had no idea Singer ever made a rotary hook machine for consumer use, and this model even has a cleated timing belt. It’s very like my Pfaff 360. I read quite a few disparaging remarks about these machines but I find it very interesting. It’s an example of Singer’s transition from 15’s to the “modern” age of zigzags and embroidery. It appears to be cast aluminum, so it’s not as heavy as I expected. One really annoying thing about it, though, is that you have to raise the machine out of the table to get at the bobbin. The sliding cover doesn't actually slide.
I popped it into the lousy table I got with the 66. The conversion went perfectly. There really wasn’t much “converting”, as all I did was to swap the motor belt for a treadle belt. My guess that the treadle or bolt-on motor setup are largely the same was correct. The machine runs strong and smooth and is easy to control with the treadle.
