[68GMCCustom]

Your right...possible entry thru intake.
Many, many years ago I was a HS senior (and later HS grad working thru comm. college) at an auto parts store back in the machine shop. Turning rotors and drums, pulling motors apart and tossing blocks/heads in the vat, beadblasting things clean, resurfacing flywheels and heads, pressing bearings and u-joints, facing and tipping valves, testing valve springs, installing new seats and guides in heads, or sometimes just knurling the valve guides instead of replacing, etc. etc.. I say this as day to day ops showed that majority of the big long 6 cyl heads we pulled apart were not always flat, and needed resurfacing...and a small percentage would have cracks between the valves.

Or at least 30+ years ago, that's the way I remember it!
Hopefully won't be the case for you tho and you'll have a good one.