An alternative strategy to refurb a vintage pump head that you suggested wasn't high end to begin with is...simply buy a different head.
I am in fact replacing the smarthead on my Topeak with a 'twinhead' made by Topeak. Attachment hose OD tends to be similar pump to pump.
They sell the combo twinhead on ebay that services both presta and Schrader valves. What I like about the twinhead versus the smarthead is...I believe the smarthead to be a bit more of a compromise by trying to fit different valve stem diameters in one head. The twinhead is two perpendicular dedicated orfices which I believe to be a better design. The smarthead and twinhead made by topeak are both rebuildable. Topeak makes the popular Joe Blow Pro..what I have and has great ergos for pumping high pressure unlike other pumps.
Good luck.