Help me diagnose why my head gasket blew

Well, we live and learn. Nothing lost here but time and money.
You have a some issues in my opinion but I don't I can be much help on one of them...
1. The build is too much for factory PCM controls. It's a very common problem - but I don't have much experience with it. My fix would be a stand alone management system and that's probably way too much money dna time. Hopefully someone with factory EFI Magnum experience can shine some light on approaches for this.
2. The machining is questionable. That you can address and hopefully the shop works with you on it.
3. Edelbrock heads suffer from what everyone's heads do - production line workmanship. The valve guide clearance is ususally all over - some really tight, some really loose. That's normally where the oil comes from. Also - the seat machining sucks so they don't always seal the cylinders as well as they could and the rocker geometry can be screwed up. I'll add the decksurfaces can be too rough for some gaskets too - although in this case I'm sure that's not an issue.
4. The assembly. Did you do this yourself or ahve a shop do it? Oil in the chambers can also come from rings, which can commonly be cause by assembling them on "dirty" bores. Did you wash the block with brushes and soapy water? Did you wipe the bores with brake cleaner and white paper towels in the directions of the honing patter until the towels came out clean? Were the head bolt holes tapped and blown clean to clean the threads? Was head bolt and dowel pin engagement checked to make sure you were torquing the head and not bottoming out the bolts?