Somic testing works,, but unfortunatly also measures rust. And normally are only used to check 12. 3. 6. 9 oclock positions in the bores. Will find bores thin on one side, may find a thick seam but unless used top to bottom can still not find weak blocks.
Had a friend here yesterday who had a [rusty] 313 Mopar the block was checked and it measured thick. Bored 035 to 318 and first time out was losing coolant and he found a hole, resleeved the hole and first time he started it it did not sound right, pulled the pan and there was a dribble from another hole! Those blocks will bore to 4", or at least good ones!
I did a 302W which again was rusty but had been a good runner. Tested ok. But the engine shop [luckily] bored it [020] Fri and came back Monday to hone it and it was showing rust marks at the bottom of the bores!
Trying to find early W blocks that will still go 020 is hard, many were reringed and have lips bigger! In the end used a late W block , a US Import and it was great, but you have to watch for the subtle changes between about 70 and 90 or you have problems.
Another shop I know kept testing blocks and discovering water when they actually bored them 030. This on Cleveland blocks. I think it was the fourth was ok!
Here in Oz far too many people [myself included] used water to cool engines. And now far too many are rusted out.
And cheapy coolants are not much better either.
And even if the blocks survive the radiators get blocked very regularly with all the rust scale.
Many racers at least use filters, socks etc to keep the crap out of the rad, though in worst case that can cause overheating as the filters clog up. Literally check them every race.