[Marcello]

"With 1950s and 1960s technology, yes; but not with 1970s and onward tank technology"

So did the designers of the 2S19, AUF-1, Palmaria, PzH 2000, AS90 etc, all post 60's stuff and none of which has armor exceeding the levels I described (judging from the information available), get it wrong ? And some of those are actually built using tank components.
I am all for standardization but sometimes it does not make sense. Using the same components (like engine and such) for maintenance ease is a good thing. But a tank and a SPA are on the opposite spectrum of the level of protection vs volume protected trade off. Unless you are designing a SPA turrett for the export market, to be mated with whatever tank hull is locally available (like the Denel T6) the approach described does not make much sense. Two 50mm layers of RHA is overkill for a SPA armor needs.