Dear Flame;
Sounds a lot like bearing clearences are to wide.
I would check the rocker assembly for leakage first however.
Then; using a quality pressure guage & a battery operated drill spin the oil pump & see what you have with SAE 30 oil @ room tempature with the side cover off.
If your block is not drilled for 'juice' lifters you could try it with them (solids) out & see if you can see/hear oil loss & each cam bearing.
If you haven't found by then It's in the "lower end" somewhere.
Good luck, John M.....
