I have a set of Shimano 600 cranks (FC-6400), and am looking for the ideal BB to pair with it. The recommended pairing long ago would have been the BB-6400, with a spindle length of 113.

An earlier model BB (BB 6207) is on ebay right now. Length is 116.

My cranks are not NOS. They show a bit of use, and often a longer spindle for older cranks is recommended because the holes have been worn a little. Is 3 mm significant, i.e., 1.5 mm per side, in terms of chainline? Is it perhaps recommended because the cranks are used? I'm building a double.

Thanks for any help!