The car was stored in a semi heated garage for 13 years and was running fine when parked.

From another thread with someone with a similar problem,

It is very common in small blocks. Just give the tops of the valves/rocker arms and pushrod seats a squirt from an oil can and fire it up. You will more oil squirting around than you know what to do with, after about three-four minutes of running.
I am very nervous about letting it run four minutes with no oil. What do you guys think?

If it was a new or rebuilt engine, I would assume the gallery plug was missing. I have changed the oil every 3000 miles and there is absolutely no sludge visible on the head.