I run a two pass aluminum radiator in my 12A and it's usually 190 to 195 when racing.
It is a custom made by Mike VanSteenberg at ISC Racing in Winter Haven. I think Mike takes a standard Howe or Griffen aluminum radiator and he cuts the header in half and welds in a bulkhead to make it a two pass instead of the typical one pass. It fits the stock Mazda shroud. I think it was about $300 when I bought it a couple of years ago. I just added an electric fan for the grid and for after the race when the temp goes up.