I would remove the intake manifold and intake valley pan and then set the intake on the heads and use a set of feeler gauges to see how much clearance you have on all four corners between intake and the heads at the top and bottom of all four corners, write those clearances down and share them with us.
As already mentioned, you may have an issue with the valley and intake not sealing up tight against the heads allowing oil to be suck into the intake manifold runners from the cam valley and the intake valley pan
![shruggy shruggy](/ubbthreads/images/graemlins/custom/shruggy.gif)
scope:
I've had that issue more than once with both B and RB as well as 426 Hemi motors: whiney:
![shruggy shruggy](/ubbthreads/images/graemlins/custom/shruggy.gif)
The good news is it is fixable, and you may learn something new with this problem
![wrench wrench](/ubbthreads/images/graemlins/custom/wrench.gif)
BTW, fixing the oiling issue will help your motor make more POWER
![grin grin](/ubbthreads/images/graemlins/custom/grin.gif)