The 1-60 Series saws (1-60, 1-61, 1-62, 1-63) were all 80cc gear drives, base on the 1-40/50 engine with the large gearcase like the one used on the 55's, 1-80's, and 800's.
The Super 55 is an 80 cc as well, a simple 55 is 72 cc, and a Super 55A is 87 cc. The 55 Series saws are the 44 (or 44A or Super 44A) engine with the large gearcase.
The 640 was an 80cc sort of hybrid, also equipped with the large gearcase.
The 650 and 660 are 87 cc and had a completely different little gearcase that tucks in almost inconspicuously behind the clutch cover. I have heard that the 660 shared the same engine block as the Super 250 but the IPL's that I have anyway have different part numbers, 62731 for the 650/660 and 83830 for the Super 250.
The 1-60 Series saws have a large, squarish fuel tank on top
The Super 55 is the same engine as the Super 44
The 640 was a sort of "in between" design, like the 440 engine with the large gearcase
The 650 and 660 saws have the small gearcase the fits behind the clutch cover
I have the full line up of the 1-60 Series saws now, just have to get my 1-61 cleaned up and put together.
I am still looking for a Super 55A, I have a good example of the Super 55 and should have enough parts on hand to complete one 55.
I have this 640; I had to repaint the gearcase so I made it black rather than try to match the existing yellow. I also have a 640 with the McCulloch bow bar that is on the shelf just waiting for attention as well.
The 650 is just for show, it will run but was in very bad shape when it came to me and I didn't really need to make it run well. One of the 660's will run and cut very well, the other needs some work as the airbox is quite loose and it won't run steady at all.
Mark