There are indeed two variants of 631 "starfish" crank. Those are the earlier variant: 1989-1994. The smallest outer ring you can fit is a 48t. The later variant (the 631/2) could take a 44t.
nice one, there is a 9106CC on the reverse, 91's then? Flookily I bought a Mavic rear mech last week blindly and it seems its also part of the grouppo . I was going Ultegra 600 with a build but I may go with these if I an source a front mech.
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My favourite use for these is as singlespeed/fixie cranks. You can remove the mounting posts from the rear of the spider and bolt a chainring on directly, as Graeme Obree did: