I actually do still own the bike - but it is in pieces. The frame, fork, and seat binder bolt along with modern components are slowly being reassembled for indoor trainer use.
I can measure any and all of the original parts, but I can't test ride it.
Test riding new bikes is certainly a good idea. But it is easy to get tricked by a short test ride. "Way back when" I put a lot of miles on the old bike. I had a lot of time to establish habits and reactions to its fit. I have give those priority over any new test ride.
Some measurements from the old bike: Stem 80mm, handlebar reach 105mm, handlebar drop 135mm.
I looks like a bike today of this same frame size might have a 100mm stem, reach of 85mm, and drop of 145mm. Thus the "in the drops squeezing the brifters" position would be about the same (80+105 = 100+85); the "hanging onto the tips and sprinting" would be a bit more aero; but the "tops of the bars" position would be a much further reach.
I'm considering a frame-up build. Right now I'm looking at frame geometries. I sort of wanted confirmation that anything with the old bike's geometry (mainly top tube length) won't work. An idea is getting a cheap frame, building up a bike with the components I want, tweaking the fit, and then finally getting a properly fitting frame. It's looking like nearly all readily available frames are identical to my old bike in the critical dimensions. That makes this a pointless exercise - I already know how it (didn't) fit.
I'll be ordering parts through the bike co-op where I volunteer. I really don't want to get a fitting and test rides from a shop where I won't be buying anything. That's like trying on shoes at a LBS and then ordering them online! I sort of have to figure this out out myself. And hey, anything I learn I can use to help fit people at the co-op.