I have successfully converted three wheelsets from tubular to clincher, keeping the same spokes in one case, just the hubs in the other two. I found a box of 4 NOS Campag. Omega 32-hole 700C clincher rims on eBay for $80, including shipping, which made the whole process economically reasonable.
When I lived in Los Angeles I had two sets of wheels (one clincher, one tubular) for my Nishiki, and I did all of my own tubular sewing. However, when I moved to San Diego County in 1981 and discovered goathead thorns, I decided it was time to switch to clinchers, which by then had become lighter weight, more response, and higher pressure than ever before.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069