The Saigas are specifically made NOT to be able to use standard geometry AK74 type magazines.
This bit of engineering allows the poly Galil mags to work great (since they're not AK mags), with the slight mods you mention.
I'm sure you can make the Galil mags work, but I suspect you'd need to to perform a major amount of mods to the mag(s) or the rifle (after which, the rifle might not be able to use standard AK mags).