Okay, here's the picture of the cam area, which is on the front to the left of the stitch width dial. A plastic housing flips up to give access. I finally tried the cams just now, and have to say I'm blown away by the elegant simplicity of this machine. I truthfully don't need the manual except for the things you rarely do, such as, does the motor need to be lubricated, and how do I go about that? I have to have a closer look at it. The flat cams can go on the shaft either way. Am I correct in assuming that if I switch them I will get a mirror image of the stitch? The first one I tried is a serpentine, and it's great.
Also, as Janey said, the model number is under the stitch length, where I had not noticed it. It's 238, but a quick look at ISMACS didn't show that model to have cams (I have barely begun looking.). Also, the letters on the front of the machine are Chinese characters, which the young man told me when I bought it, but like a dope I failed to ask him for a translation. When I first saw the pictures on Craigslist I thought that it said t-15, and assumed it would be a clone, but then I noticed the tension disk on the front. There is a knob on the left side also, but that's the foot pressure adjustment. One other neat thing is that it shows the stitch length in mm as well as the number of stitches per inch, which a lot of machines don't show. You feel like the person who designed this one actually had some experience sewing, which is frequently not the case with almost any sewing machine, or for that matter, other appliance I've ever had.
It has a low shank. The bobbin winder works and seems to have a new tire. It it exceptionally quiet, and I believe they kept it well oiled, but when I ran it with the cam engaged there was a bit of odor, such as from old oil and parts that had not turned in a long time. I will have to give it some more attention before I run it again. There's a certain amount of yellow crud on the body and especially on knobs and in crevices. The little green tag says that it was shipped with a coat of oil and to wipe it off before sewing. I suspect it's that that turned yellow with age and looks nasty now. I'll have to take off some knobs and clean them, and that sort of thing, but overall it seems to have had little wear and tear. Thanks for looking!