Originally Posted by
Garthr
Shimano UN-54/55 are not designed to be adjustable in chainline, that's why the have the lip on the left cup.
Yep, I agree. I would not attempt to use spacers with the UN55 unless I shimmed the left side cup to fit snugly around the cartridge. The contact between the cup and cartridge only begins within about 1/2 a mm before the lip bear against the face of the BB shell. With even a single 1mm spacer the left side of the cartridge would be hanging free and supported only by right side threads.
If I needed several spacers to correct the chainline I might use the 73mm UN55 if all the arithmetic worked out.