I'd be interested in looking at the snowmobile pressure filler cap. Could you please post a link to the ebay store.

The 855 cummins without a turbo had a passage in the head from the intake to the oil gallery. It was about a 1/8th inch in dia. the rocker box continued the passage to just under the valve cover. Maybe these engines have a similar passage.

When swapping out the heads if you forgot to plug this passage on a turbo engine, you could loose a LOT of oil as the boost pressure filled the crankcase.