[quickjack]

The Dart block David posted is generally used in blown alcohol applications making about 3000 HP, so usage wise it is not really a direct comparrison to the Kirkham piece which is not intended to support that kind of abuse.

Cast aluminum has a typical elongation of about 2% before failure, whereas billet has about 10%, so the billet blocks are way stronger than a comparable casting. I think at the intended power levels, the ribs likely are not a big issue.