I have 3 sets of cranks I will be installing in the near future and don't have bottom bracket specs for any of them. I can determine shell width and taper but I struggle figuring out what spindle length I need. Is there a way to determine this through measuring? I'm assuming you'd try to calculate what it would take to get 43.5mm chainline but I'm not sure how to go about doing this without being able to properly mount the cranks.

Up to now I've poured through pages online looking for this information. I've managed to get close this way but too many times it's through trial and error with multiple BBs. I'm certainly open to a more effective way of doing this. Thanks for any help!