27 inch Wheels?
 

I acquired a 1971 Gitane TdF with some nice Mavic G 40 wheels which I think can be salvaged. But....the rims have a sticker at reads "27x1 1/2". So, these are not 700c, correct? And may not work with a future (yet to be determined) frame?

Correct. They need 4mm more clearance than 700c wheels.

Current tire selection more limited in 630 (27") than 622 (700c)

8 is diameter difference, 4 is the radius difference..

Sure sounds like that would be 630 mm Bead Seat Diameter, as opposed to 622 mm BSD for 700C wheels.
Whether or not they’ll work in another frame/fork is anybody’s guess.
They’re unlikely to work in a frame/fork intended for 700C, narrow-tire wheels.
Might work in a fork/frame intended for 700C and mid-width tires.

And though it should be obvious from the other posts here already, I'll mention that they need different tires.

G40's are traditional skinny clincher rims, so slightly less than the 13mm inside width of the later MA40.
These are not the easiest rims to mount tires on!