I agree that it's a very nice find. Be aware that the grease for the bearings will likely be thick and nearly solid after having sat unused for so long. Not to rain on your parade, but it's quite possible there is some pitting on the cones and races of the hubs and/or the BB. Be sure to check those.

If you haven't already, go through Sheldon's site for all things eccentrically French. I don't know when the French started standardizing their threading and the like, but probably not by '78. Your LBS will be your friend here on those cranks which are quite possibly 23mm or 23.35mm thread.

Also, if it were me, I'd put the fattest tire I could on there and keep the pressures as low as comfortable - the ride will be dreamy. 700c or 27" rims?

Be sure to post pics. There's a whole "Post your French bike" thread.