I have a Fluidyne radiator and a 170 'stat. I think I got the 'stat from AO Engineering, but that was a long time ago and I can't remember for sure. I've also used the Stant 180...great product.
Fluidyne no longer makes the 90-96 C4 radiator, but back when they did (98-04), I was involved with the development and validation of the product back in the 96-97 period. We did hot weather testing in the Palm Springs CA area. Back then, Jim Van Dorn's "Automasters" was in nearby Palm Desert and we used his shop as a base during the testing...mainly because he was air conditioned and had cold beer.
Nowadays, Van Dorn is a cranky old bastard who lives in Bowling Green with a Beagle.
But, I digress....
I don't drill thermostats. Waste of time.
I was cracking a joke in asking the question.
In theory, drilling little holes in 'stats, might change the flow through the coolant bypass, but in practice, ie: getting a significant reduction in ECT during long periods of WOT, the idea is BS. The amount of flow through those tiny holes compared to the flow though the much larger bypass makes the holes a minor influence in a practical sense.
I think the only way to gain a significant improvement in sustained WOT ECT is to restrict or block the coolant bypass and to do that, you have to raise the system working pressure to the point that the OE radiators, some OE-replacement hoses and some hose clamps would fail.
To restrict or block the bypass, you first need to have a system that will be reliable at 20-25 lbs pressure. Then you have to have an aftermarket radiator which is reliable at a higher pressure and you have to have a way to upgrade hose retention such that its reliable at the higher pressure. Older engines may also have issues with head gasket sealing between water passages cylinders at 20-25 psi.
That pressure level in transient spikes might even be higher, too. Back when Fluidyne was still building it's radiator for late C4, after we brought the product to market, I started a test program to investigate restricting or plugging the LT5's coolant bypass. I installed a coolant pressure gauge in the system and had some Delrin restrictors and plugs made for the bypass. The Fluidyne guys were confident, based on their building NASCAR Cup radiators, that the radiator would handle the pressure. It was the hoses and clamps we were wrestling with when I pulled the plug on the project due to lack of my time and Fluidyne budget cuts. At the time, I'd settled on a 27 psi radiator cap and restricting the bypass to approximately half its original flow as a first step.