Originally Posted by auchencrow

Rusty chain? Replace it. And if you replace the chain you'll need to replace the FW 95% of the time or you'll experience skipping under load.
There is nothing tricky about French FWs - There are the uncommon, older, French market threaded hubs, but the ones you'll likely encounter will conform with the standards popular in markets they were intended for. Also by '78, Moto was using a lot of Japanese components anyway.

I would recommend a hyperglide 5-speed Sunrace FW. They're inexpensive and function very well.

I would recommend 27x1-1/8" Panaracer Paselas - They're a nice compromise between smooth rolling and smooth riding characteristics.

You will need to service the bottom bracket with new ball bearings and grease - but in the unlikely event that the cups need to be replaced (and if the ARE french threaded by '78) there are plenty of spare parts available. It's the intermediate Swiss threading that can cause headaches, but even these can be addressed with new Grand Crue cartridge bbs. Again - if it was not being ridden, it is unlikely that you will need to replace anything (unless you start riding it yourself without first servicing the bearings - including the bb, hubs and headset)