This might be a good time to switch to 700c. Also is your Jubilee set at 120 mm or 126 mm in the rear? This might also be a good time to spread the rear triangle to 126 so you can run 6 or 7 on the back.
You may, however, prefer to build on the old hubs and keep it at 120. One thing to keep in mind is that cones for those hubs are difficult if not impossible to get. You will want to overhaul the hubs before rebuilding the wheels to make sure that the cups and cones are in good shape. If they are pitted, it's likely time for new hubs.
New hubs designed for 120/126 spacing are available. Velo orange sells a hub that can take a freewheel:
https://velo-orange.com/collections/...heel-hub-126mm
Suntour XCD hubs are pretty slick and come in 120 OLD.
Personally I'd seriously think about building new wheels around the velo orange hubs using TB14 H plus on rims even if that means spreading the frame.
TB14 | H PLUS SON
There are other silver rims out there as well but the TB14s look nicely old school.
If building new wheels, I'd find a good freewheel as well. IRD sells 5, 6, and 7 speed freewheels:
Classica Freewheels 5/6/7-Speed ? Interloc Racing Design / IRD
You'll end up with a heck of a nice set of wheels and the shifting will improve to boot.