Someone asked me about fitting 800 cams into a 750 motor, so given I have 620 and 750 cams easily at hand I figured I'd take a photo and make it a bit clearer.
Prior to the 620 and 800 motors being introduced, all the cams since Pantah run with two bearings at the pulley end and one in the cap. Part of the 620 and 800 minor redo was to drop one of the pulley end bearings. The cap end is also different, with about 3 or 4mm added. The form is the same, it's just longer.
To fit a 3 bearing cam into a 2 bearing motor you just need some spacers to position the cam correctly at the pulley end, as the cam is pulled to the pulley end when tightened.
But to fit a 2 bearing cam into a 3 bearing head you need to grind the cam to locate the larger, inner bearing at the pulley end (as it sits next to the lobe) and also shorten both the snout and spacer section at the cap end. I don't think you could just add another bearing further in at the pulley end, as the head is machined to locate the outer bearing in its position. I think, I'd have to look now that I'm saying it to remind myself.
Anyway, photo below. 750 at front, 620 at rear.