I'll third this practice.
I've been using Castrol RX Super (now called Castrol Diesel) 15W-40 in a bunch of older cars that I've owned over the past 10 years or so. Some of the cars were foreign, some domestic models, some 4 cyls, some V-8's. Something about the additive package in these oils works amazingly well in older motors that are in reasonably good working order. The cars I used (and continue to use) it in are mostly 1960's and 1970's vintage, and don't see lots of miles...more sitting. I've recently tried some DELO 400 15W-40 in (ironically) a 73 Mopar 340, and it seems to be working excellent so far.
Once the steady diet of these oil was begun on a particular car, I noticed significantly cleaner running and cleaner exhaust (no visable smoke), less (or none) external oil leaking, and markedly less oil consumption.
Acewiza....I'd stay away from syn in an older motor. When I tried AGIP SINT (synthetic) in a '76 Ferrari 308 it was not good. Lots of consumption, lots of exhaust smoke under hard acceleration. My mechanic suggested that the synthetic oil was probably causing issues with seals, specifically the valve seals and lots of oil was breaching them and being burned. I agree with that. I then went to the Castrol RX Super because it had worked so well in other older motors in the past and the results were much better. I continued using it for years in that car.