One of the BB bearings went out on my Ross road bike, I would like to convert to a sealed cartridge unit, but I don't understand the numbers I'm getting for measurements.

It has reverse threads on the drive side, so it's english. However it is 70mm wide. I read that I could just go with a 73mm and get some spacers, but I also can't find the length of spindle I need (it measures 125mm, 32-55-38) I have it apart and didn't check the clearances for the chain ring. It has 2 rings on front, and uses a square taper spindle.

Can someone recommend, or just point me in the right direction, a sealed cartridge unit I can use? Or sell me a used one?

I was looking at a Shimano UN55 square taper bottom bracket from Chain reaction cycles (sorry no link, not enough posts). I figured my best option would be the 73x 122.5mm. If I got a 3mm spacer would that also make up for the offset crank?

Thanks, Matt