New engine has loss of compression

If the heads were just installed when new, that's part of the problem I'm sure. The valve job on a shaft rocker system sets the geometry, which in turn provides either normal wear or poor geometry and faster wear. If the bore in that weaker hole looks good, and the piston is not damaged on the ring land, I'd say it was the heads. The Edelbrock springs hsould have been good enough for the XE268. Maybe not perfect, but usable. So my feeling is it's probably the valve job issues that led to the sealing problem. Wise choice to bring them somewhere.