...I can't remember if it was the Sugino Maxy cranks, or the Mighty cranks (or both), but I dimly recall that the square taper sockets on those were not JIS taper ( I think)...I'd have to research it to be certain without looking at your parts.

Try searching for that information, and look at the actual fit of the cranks on your cartridge spindle. If the fit is OK (not bottoming out or in danger of doing so), I would personally just get next step up (longer...or whatever you need for chainline on the drive side) and call it good.

Q factor doesn't seem to bother me much, even though I hear people go on and on about it.