Looks like panaracer has a pretty decent selection of 650b road tires. The gravel king 650b x 38c look like a fine tire and the weight is very good at 310 grams, https://www.panaracer.com/lineup/gravel.html

I haven't decided on the rims yet but I'll probably get the soma weymouth rims. They're siilver and they'll look right on a vintage bike. They look like pretty tough rims if a bit heavy at 580 grams, Weymouth Rim (700c & 650b) | SOMA Fabrications. Still I'd prefer something a bit lighter. I wish sun CR 18s came in 650b size.

I'll have to decide whether to use older hubs and stick with 126mm in the rear or stretch that frame to 130.