Hm, an old Nervar should be ISO sized on the taper, and the Downtube will almost assuredly have a JIS taper crank.

If my suspicions in that regard are correct, the ISO Nervar will sit about 4.5mm farther out than usual on your JIS taper bottom bracket that the Nova will have. It is okay to use this combination, if the chainline ends up working out for you in the end. Let us know how it goes!