largest stack plate one you can fit (not sure what sizes are available but might need to plumb 2 in series). I will defer to Kunkel on this but if the internal cooling fluid passages in/out behind the 2 brass fittings are larger than the brass fitting ID itself then could go to larger fittings and 3/8" lines for more flow (along w a 3/8" cooler of course). Even on a streeter I use the largest surface area I can & I am not convinced a trans can run too cool EDIT but w you being a dragger being too cool is not even an issue