Italian bottom brackets and modern cranksets - a compatibility guide?

Question

I have an Italian frame (presumably a Moser) which I chose to repurpose as a single-speed/fixie with parts from another Single-speed/fixie of mine, with the exception of the bottom bracket and crankset, due to the size difference.
I chose to go with a tapered / squared JIS axle, but the spindle length in relation to both the crankset and the chain line is still making me confused, being the first time I have to buy these parts, therefore:

what should I take in consideration when looking to pair an Italian BB with a crankset?
is my current chain line measurement (on the older bike) of any use when looking for these parts, since those same wheels on the old bike will be used on this Italian frame? (taking in consideration the wheel's axle length and how much the cassette can be moved using spacers)
is it better to buy a BB with a spindle length longer than the one recommended by the crankset manufacturer or shorter?

Nathan Knutson · Accepted Answer

Spindle length and chainline are immaterial to it being Italian. The center of the spindle is at the center of the shell either way. If the chainline is good now and you're using all the same parts, get another JIS BB of the same spindle length in Italian.
If you wanted to tweak the chainline, it's the same process as any square taper crank. Use your existing crank and BB to figure out what length spindle puts the chainline where, figure out the chainline you want, and change the spindle length by twice the difference.

Italian bottom brackets and modern cranksets - a compatibility guide?

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