[blueosprey90]

Greg, I run a plastic radiator shroud on my MGA (stock puller fan) and it makes a big difference in how much air is pulled through when compared to no shroud - at least when the car is sitting still. At speed, I suspect it has less effect since the air is otherwise being pushed through the radiator by the car's movement.

My shroud and fan tip separation is quite tight, maybe only 1/4".

I can't remember what drives the water pump on my PV444, but assuming that your water pump is driven by a pulley, it might be worth considering a larger pump pulley. The theory is that if you slow down the water pump, that will slow down the water moving through the radiator and allow it to cool longer before returning to the engine. I suppose a whole course in thermodynamics would be necessary to evaluate flow rates, temperature differential and heat exchange, but I believe that this would work better at faster speed rather than slower.