The Wheel-A-Brator I mentioned does exactly that - picture a rotisserie inside a cage with shot being thrown as the part rotates.
Never had issue with blast media left in the engine - rifle brush the oil passages, run water through the coolant passages.
I always knock out the core plugs and remove the gallery plugs before getting a block blasted.
The machines I have used did nothing that required getting the block machined again, just honing the bores. I think it relates to the media being used.
I have seen some blocks with mild peening of machined surfaces.  I used this setup when I was doing machine work. Bake the block for about an hour to make sure all grease and oil was dried and turned to powder. After blasting, they come out looking like new castings. If you don't bake them prior to blasting, the blasting media will just cake up and lodge in the oil galleys.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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