The bike is fine to ride, but it's been sitting for a long time so you will need to have everything regreased and lubed because the grease gets stiff over time, and I mean everything, failure to do so could ruin bearing, not that those can't be replaced, but why if you can avoid it?
I ran into the same situation about a year ago when I found a 77 Raleigh Competition GS leaning up against a dumpster, the paint and components were in extremely good shape, all that was wrong was the headset was frozen. Took it home, got the headset out, cleaned it up and the bearings looked fine, so, I re-lubed it she runs very smooth, then I relubed everything and found stiff grease in the BB and the hubs. The bike ran great except the Campy GS derailleur stuff never worked great even back in 77, I was familiar with that stuff, so since I had a set of brand new Campy Nuovo Record derailleurs I bought brand new in 76, 77, or 78 that I got on a stupidly low-price sale, and never used the stuff, I put those on and the bike shifts great now. I also had a set of used Campy brakes from the same period, so I took off the Weinman Carrera brakes and put the Campy on instead so now the entire bike is Campy. I kept all the original stuff of course. That bike I found had very low miles on it, the saddle was the original Brooks Professional that was never broken in because there are no butt bone indentations in the leather.
Anyway, just get it relubed and regreased BEFORE you ride it. And while you're at it make sure you can get the seat post out, then put a thin film of grease on the post and on the inside of the seat tube to prevent the seat post from ever rusting into the seat tube.