It would be good to see that flow schema

I have had a 2.5 V6 in pieces in front of me and the flow path wasn't obvious

I don't imagine the block is the main problem. The things that struck me were:
- The water pump seems quite small
- The coolant bridge must be very restrictive (but I don't know if that matters)
- I couldn't see where the flow through the oil cooler comes from or goes to.
I think the pump pulls coolant from the block through two passage (one from each bank). The coolant then appears to go up to the thermostat and probably goes through the heads and/or oil cooler to the rear. The coolant bridge lets water out at the rear of the heads that goes through the HBV (& cabin heater) and then tees into the stainless pipe from the bottom of the radiator just before it connects to the rear of the block.
The two areas most likely to be vulnerable to overheating would be the cylinder heads (distortion, gasket failure, valve damage, pre-ignition) and bearings due to over-heated oil.
I imagine the easiest way to deal with the high oil temperature would be to use fully synthetic oil.
One alternative might be to fit an external oil cooler and then re-route the coolant flow that currently goes through the oil cooler to improve the flow through the cylinder heads.
Another alternative might be to add an electric pump something like this
Demon tweeks electric pump.jpg)