what oil filter are you using? some have anti-drain check valves and some don't. could be that your oil galleys are bleeding down through the oil pump after sitting for a while?

0* timing on a Cleveland? must be a real dog set that way, i don't think any Cleveland ever came with a sticker that specified 0* timing.

i'm curious what the total timing is set at 0* ?

i would install a timing tape on the balancer, set it for 36* total and see how she flies.

total timing is set with the vacuum disconnected and plugged, run the rpm up steadily until the timing light shows no further advance, then turn the distributor to adjust. you can let the engine idle or shut it off to make the distributor adjustment, then bring it back up to rpm to check the setting.