Can't see why you couldn't. You would need new fork and headset, stem and bars, plus any spacers. Unless the frame is an old Le Champion, that's more $ than the frame is likely worth. And if it is an old Le Champion, I wouldn't (I couldn't) change it like that. That's me, tho.

If the moto is a prime one (Le Champion, 70s Grand Record, 70s Grand Jubilee) I wouldn't mess with it, try to keep it pretty close to original.

However: The prime rule in working with a vintage bike is to not do anything that can't be reversed. Don't cut off derailleur hangers or braze ons, that way, if the vintage bug bites you, you can take it back to original or something close. Switching over the headset and fork can be reversed.