Well, received my replacement board and block today, so here goes board #3, block #2 and attempt #18...

@tiborr:

Any suggestions apart from NOT using the NB foam protector?

I'm still not happy leaving the SMCs of the NB exposed under a huge block of copper, so I suppose I'll cover them with kapton tape (is 0.07 mm thick so I sincerely doubt it will have any impact on the mount at all and it gives me peace of mind...)

I would really appreciate any constructive directions as I'm starting to feel rather inadequate after all this hardware destruction and failed mounts.