I'm looking to replace my bottom bracket + crankset on a mid-1980's Trek 830. It has a 68mm shell with the standard 24 threads/inch, so I'm good there.

Have decided to go with a Shimano UN54 BB but am unsure about what spindle length to choose. My spindle from the original "cup and cone" BB measures ~126mm (see picture). It's a "3T" designation, from Japan, as mentioned by Sheldon Brown.

If I go with a Shimano 7/8 22/32/42 crankset, I've seen it written that a 110mm or 113mm BB spindle is required.

Which spindle length do I go with? Close as possible to the original length or the one recommended/required by the crankset?

Thanks a lot!