Finally, on the fifth attempt, I found a Clevo block that sonic-tested good. The thinnest reading was .131" (just over 3mm). The best part is that I bought it for $50 on Ebay, sight unseen! Just goes to show that they can turn up anywhere.
While at my parts supplier today, I also saw the sonic reports on 2 XE coded 4-bolt blocks. Both tested worse than the worst Clevo I had tested. Both had less than .070" wall thickness. Someone's going to be very disappointed, considering XE 4-bolts sell for $1500 to $2500.
At least I can start my engine re-build now. No doubt I will have a few questions & will be seeking advice from you blokes/girls.