Are you running an electric water pump?
There used to be a guy John Bennet [retired] who enhanced OE water pumps from using pi$$y little pressed steel fans to using actual impellors.
He also had parts made to house the thermostat in the bottom hose. I hope I can find all his Paper work, this same guy designed the cooling systems on the V8 race cars.
He may have a web site not sure but a very talented guy with heaps of knowledge gone to waste. I had one of his systems on my cast iron 350 chev 4x4, you could idle all day with the aircon on,
that's how good his system was, He had systems to suit motor HP motors