Noisy bottom timing chains, worn big end and main bearing shells, (the former often caused by the latter) oil leaks from the rear of the head gasket ("O" ring), rusted sideplates, corroded cylinder heads.
Take the plugs out and leave some lubricant down the bores a good while before you start it, then crank it over with the plugs out to get the oil pressure up before you finally try to get it running. After that make sure the thermostat isn't jammed shut and wait to see what happens. There are plenty of things that could happen, but best to see what does happen before worrying yourself.