i just bought a 78 chevy custom deluxe 20 /2 wheel drive, granny 4 speed and a 350

. i got it going and its runnin pretty decent- it had been sitting for 3-4 years. yesterday when it was running i noticed the oil pressure would jump around really quick and then kinda settle down and just show normal pressure. tonite when i started it up it goes all the way past 60 when the engine is turning over then once its started it shows nothing at all. any ideas about wuts going on?