Measuring chainline without cranks? I just bought a 1970s Peugeot Mixte UE-18 for $10 at my local bike co-op. It's in great shape, but is missing the bottom bracket and cranks. I'd like to upgrade to a cotterless crankset. However, I don't know how to measure the chainline without cranks installed. I was thinking of getting these BB cups (with French threading) and finding a spindle of the right size. How do I figure out the right spindle length? Has anyone encountered this issue? Am I going about it the correct way? I would just like to keep the cost of the bottom bracket under $50. 

Thanks in advance!
You can measure the chainline at the cassette as well as at the cranks.

Park tool Company has a nice article on measuring chainline at both the crank and cassette.

https://www.parktool.com/blog/repair-help/chainline-concepts#article-section-3

It's my understanding that bikes sometimes have the chain further offset from the  frame centerline at the crank than at the cassette, to avoid the chain rubbing on the next bigger ring when small ring - small sprocket cross-chaining (triples especially).