Intake manifold pulling oil

You might have already done this but…
Use the pin end of your calipers to measure the bolt holes in the block then calculate the difference on your heads/bolt length.
Might be a possibility the head bolts are bottoming out causing an improper torque and a loose head/gasket.

Also another possibility could be the head bolt holes in the block go through to the water jacket and need proper sealant on the threads.
A long shot but worth checking it with the verniers again using the same method, check all head bolt holes in the block for water jackets/coolant passages.
I know this is 318 but ya never know…could be 360 also of the same year.
A 360 engine gasket kit might have had the same bulletin.

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Another stupid question; are the locating dowels still in the block for the heads to line up?