54mm chainline

nothing in a 73 shell unfortunately - here;s my thinking along those lines though...

a sugion RD needs a 103 JIS spindle for 42mm chainline
so... i need to increase the chainline by 12mm which means increasing the spindle length by 24mm - voila - 127mm spindle... sound sensible?

I think i'll just order them then work from there with spacers etc - i've got both chainring spacers (decrease chainline) and bolt on cog spacers (increase chainline) so we'll see. Are the spindles in a un54 interchangeable?

Sounds sensible. Spindles in most modern bottom brackets are not interchangeable. The UN bbs along wth most square taper cartridge types and octalink, isis and powerspline are all sealed units comprising threaded cups, bearings and axle. More modern Ex or X or external bbs are just cups with bearings, the spindle is permanently attached to the (usually) driveside crank arm