First of all, many thanks for the thoughtful comments received. A few thoughts in reply . . .

• Sunshine 5345s seem to be pretty ubiquitous and not too costly on eBay. Every 10/12 speed I see has them, other than my awful old Ross which had low-end Maillard hubs. Near me is an outfit called Bike Saviors which helps folks repair and build bikes. Their prices are good on individual components - maybe there's one like them near you?
• Why did I use Schraders? I confirm the aesthetic appeal of Presta and the purity but it's a pain unscrewing the little top nut on the core and fitting the adapter so I can use a compressor or standard car tire pump - and then not losing the adapter. A related point, I have yet to find a truly easy or effective inflator chuck fitted to a "stirrup" pump. Always a struggle, with more pressure lost putting it on than seems right. BTW, the Maillard wheels came with Schrader piercings . . .
• The H+Son rims include a maker's plate held in place at the valve piercing. A part of the decision to remove it was that I had never seen such a plate on my '70s and '80s machines and as it's only held in the center it could trap grit. My old wheels usually had a decal artfully covering a rubbish pinned joint, even on quite good rims (yes, Mavic). If you go this route, thread some green "Frog" (low-residue) tape under the free ends of the oval plate and on top so that when it begins to loosen and inclined to rotate the tape prevents scratching the polished finish on the saddle of the rim. Removing it reveals a correctly-sized Schrader piercing.
• Regarding the counterbalance, another very good point. To check, I put the Fuji up on a stand, and looked for balance issues - did the wheel stop spinning with the valve at the lowest point? It didn't, and was pleasingly random with a slight tendency on one wheel to stop with the valve at a horizontal position.
• Encouraging observations from AngryScientist and Andy K about the tires, and I am sure you are right about the ride and hope they loosen up a bit as mentioned. For comparison, I have another set with Sunshine Sheriff Star hubs - much liked by the great Sheldon Brown - and TB14 rims, on which I mounted Veloflex Corsa Evo 25s, the wheelset intended for an '86 Team Fuji frame I was graciously given by another C&V member. The wheelset gives a bone-shaker ride on urban blacktop, just plain unpleasant. What a costly experiment!

It's dialogs like this that make my $20 for two years well worth it.