I believe the High/low shank is more age based than model. I was only looking a specific features (like stretch or "variegated" -the ability to make a stich that moves forward and backward along with side to side) and all the machines that did that were super high shank. All those I looked at that were low shank were much earlier models. So I came away with the "feeling" that most of the 158 group were super high shank.
I do know that there are at least three different attachment sets, and all machines take the single row cams. Only the newer with the variegated ability can use the double row cams (these go both side to side AND forward/backwards)
it "sort of" seems like the models ran in series - so one year Sears would offer a 15XX, 17XX and 18XX machines, and the next year they'd have an updated model, and it would be a 15XY, 17XY and 18XY machines. So having two machines that both start with "17" may actually be significantly different because they are several years apart.