Speedmaster set up their product to run a taller installed height. Speedmaster are a bolt on head but it IS NOT an OEM spec piece. Lunati recommends a spring that is suitable for the shorter OEM installed height.
Blame whoever you like. This is part of being a competent engine builder. You either shim the crap out of the lunati spring or find a spring with a suitable seat pressure and compression rate.
If a shop can't figure this out, they aren't very good. It's the shops issue to come up with a suggestion/solution. Don't expect lunati to assist if things go wrong using a different spring.
Yeah phone tech support with most of the place sucks now. That is spot on.