Wrong-o-steve-o RUSA just replaced the former organization. I was/am a member of both. It definitely wasn't as big then as it is today (thanks in large part to RUSA) but it was pretty healthy. Especially here in CA. If I remember correctly, the Davis bike club alone had over 100 riders do PBP in 1995.

Regarding the OP I started doing brevets on a 79 Peugeot Competition lite with all the original Stronglite components. It worked pretty good but it really beat the crap out of me (I didn't know how bad it was until I modernized my ride). Plus I was striving for better performance so after a while I decided to buy something new. All of these bikes I've ridden 600k or longer brevets on including the Peugeot. The first "new" bike I bought was a Colnago Ovalmaster (TI), then a Merlin Extralight(TI), a Cannondale CAAD9(AL), a Specialized Allez Pro(AL), then back to Colnago with a C-40HP (carbon). My C-40HP was destroyed in a high wind incident and my insurance replaced it with a C-50 (also carbon). That's the bike I've been doing brevets on for a number of years now. For me it's the ultimate brevet bike. It definitely has the very best, least fatiguing ride of any bike I've owned or ridden. There is nothing like getting off a bike after a 1200k and feel good enough to turn around and do it again! For me, vintage is cool, I still have the Peugeot, but for long brevets I'll stick with my Colnago. In fact, it you'll notice I road steel, TI and AL bikes on 600K+ rides and for those long rides I won't ride anything but carbon anymore. For a double century or shorter anything goes but for longer distances carbons it.
I'll add a pic too. Cruising with the C-50 on the Cascade 1200k