Vintage Peugeot conversion help and tips please

The BB won't work, it will be English threaded, your bike is French threaded. Threadless BB should be £15-20 and you will be laughing, get the shortest spindle length one you can find it will make chain line easier. You will have no problems putting a 120mm track hub into the frame, might need to much around with a spacer or 2 to get the chain line right but thats about it.

it depend on which peugeot it is, some peugeot are english threaded like mine.

my rear wheel wasn't mavic open pro, it's Mavic CXP33s, still decent rims mind, but the open pro suited the bike better than a deep V rims.