les grip and i ran about the same engine setups. i ran a s/c and then passed it to grip. oddly he ran higher temps than i did. whats the difference? look at the slk32 grill and yours. we had huge open space that you dont. look at the slk32 lower bumper and yours. more open space. fwiw thats the difference. airflow. building a tank will help only if you can provide enough ice to last the entire run. if not then as soon as the ice melts the temps will become ambient or more. you can have a 10 gal. tank it wont matter. you could rig a tank loaded with alcohol and a switch to spray the h/e when temps start to rise but it wont last for long.
sadly you live in a hot climate and race for longer than most any other kind of race. its a double dagger to your cooling system

fwiw i also ran higher ect temps. lowered them with a 180 tstat and 180 fan mod. it helped until aug and then eng temps were 200* on a consistent basis