I've 'done' water spray on a buried radiator in a prototype amphibious vehicle. Worked great, with just a shower head and a cheap motor home water pump. You may not get the shower head far enough away to get max coverage. Try to obtain/make some simple spray bars.
A serious caution: Use distilled water. Tap water will absolutely foul the aftercooler and radiator. Common problem with older tour buses going over the Rockies to Reno. The old Detroit Diesels were so very inefficient/poorly cooled that that was they only way they could make it was with (tap) water spray. (I built a Silver Eagle Bus motor home, and installed a modern Cummins Diesel).
Enjoy /s/ Bob