Did you not say that the liners had dropped a little in the block?
That could well be the problem.
A good few years ago I had a very similar problem with the antifreeze getting blown out the header tank. Spent hours messing about with the rad making sure max air flow went through the rad. Did a comperssion test which showed nothing wrong but still couldn't keep the thing cool. Finally tore the heads off. No easy task in a V8 SIIa hybrid and found the faintest discolouration on the head gasket. Sure enough when the engine got hot a small amount of compression was leaking into the waterway right at the back if the left hand cylinder bank and pressuring up the system. New headgaskets cured it in that instance.
Diesels.....great when they're going and so easy to work on.