Quote:
"As per standards published in 2003 by ASTM, an international building standards non-profit, all concrete blocks must support at least 1,700 pounds of weight per square inch (PSI). This standard only describes minimum requirements, however."
I don't see how lateral stability is any worse than 4 jackstands. I wouldn't hesitate to use CONCRETE blocks (not cinder blocks) to support a body. They need to be used with the holes vertically oriented for strength. I'd even work under the car supported that way. No worse than jackstands.
I was under the perhaps misguided (or perhaps not) impression that a concrete block and a cinder block are the same thing. I found that for the most part they are not. Cinder blocks are made from cement and fly ash. Concrete blocks are made from concrete - however the concrete composition can contain fly ash. And yes there's an ASTM spec for concrete blocks, but are all "concrete blocks" made to ASTM standards? I really doubt it. I did find a comment by a civil engineer saying that you should consider them the same unless it's known otherwise.