I really don't understand the need for huge chunks of concrete, my slab is eight inches thick with regular concrete screen in it, my frame is eight inch square steel tube with half inch plate on the top, the frame is setting on four rubber vibration isolators from McMaster Carr, I think they are rated at like 900 lbs each and my 8/1 is happy as a clam.
The trick is to tame the engine with a good balance job, then they don't need five tons of concrete.