As you haven't got a BB (as you don't know which to get!) then you cannot measure it. If the rear is 45 and you mount chainring on outside with a 107 then it would be close enough. One option is to try and get a very cheap 107 and try it out.
@kerley started
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As you haven't got a BB (as you don't know which to get!) then you cannot measure it.
If the rear is 45 and you mount chainring on outside with a 107 then it would be close enough.
One option is to try and get a very cheap 107 and try it out.