I think I'd try restricting the flow rate a little, to give the coolant more time in the radiator. Don't overdo it- - - -mabe reduce the diameter of the hole in the thermostat housing by 3/8" or so, maybe 1/2" at most. Online racers' supply places like JEGS of Summit will have the reducer washers in whatever size fits the housing. I've made a little more durable ones from a piece of 1/8" thick aluminum with the edge thinned down to fit the counterbore in the housing.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!