Adam,

Welcome to BF and C&V.

Unfortunately it can be very difficult to know what the threading is from your original description. Sometimes French made parts and bikes imported directly into the US came with ISO or British threading. Other times they came with French threading. Sometimes the parts are marked with a code which reveals the threading, other times they are not.

Pictures can be helpful. Look on the back of the freewheel for any symbol marks or writing. Also check the hub, usually just between the threads and the flange on the drive side.

Best of luck and we look forward to seeing your bike.