Almost no tolerance for surface metal removal if warpage exists. On those heads.

A little history perhaps. The early 603 3 liter engines had an excellent lower block. The problematic head caused the engine to be withdrawn from production for a few years. Then they over bored the block to 3.5 liter and put a very refined head on it to release that engine again. The heads where great but the 3.5 lower blocks had major issues.

So that engine was withdrawn as well. Yet a 3 liter block with the 3.5 head is an excellent almost bulletproof engine. My guess and it is only a guess is the better 3.5 liter heads may be easier to source now than they have been for some time. As I suspect demand is down.

To add to the general misery it is felt that the # 14 head does not like to be overheated much.