My GTS has a 160 deg Mr. Gasket high flow thermostat. EMP also sells the Robert Shaw version which could be the same idk. Both (last time I ordered stock) have high flow bypass valves. I used an aluminum 22" e body radiator (KkS brand) off of ebay with two 10" fans switched off of a coolant temp sensor (Summit brand) that grounds out the fan relay at 185 and opens the circuit at 165 deg F.
Typically I roll into the burn out with the oil temp up at about 140-150 and stage around 160ish. It has never gone over 190 on the return road (single pass). Last t'nt I made four hot lap runs and never saw over 195 on the return road.
If it was me I would drill/tap the w/p housing and install a bypass. I'd think -8 would be more than enough. You could bend the line out of aluminum if you choose.
I don't like the idea of water not circulating and also would avoid deadheading the pump.
Popping the w/p manifold off and milling out a hole + tapping sounds like a relatively simple solution. The most painful aspect of the job is prcing out AN fittings. Aeroquip push-lok fitting are compact in comparison to the conventional style unless you are talking XRP or one of the upper echelon brands.
Dumb q:
Did we verify the temp with an infrared temp gun or other means of independent comparison? What was the ambient temp?
While I do think water temp is important I'd be more concerned about oil temperature in a drag car. In my experience takes quite a while for the oil to reach operating temperature after the coolant has done so.