Hmmm, a bit further googling and I may have answered my own question.
This website says:
Shimano LX 74/100 BCD FC-M560 1993-94 113mm x 68mm - English 118mm x 73mm- English
I have a used 115x68 cartridge bb laying around as well as a 117.5 spindle and a couple of sets of cup and cones. I think I'll give the 115 a try as I doubt 2 mm will make that much difference in a 3x8 speed derailleured bike, right?
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"