I think they're to stop reversion back through the MAF sensor, which would otherwise read the same air twice. The later 20Vs don't run a MAF sensor so I dunno what they do in that case, but normally ya rip the airbox off altogether and run open ITBs so it doesn't matter.
That's quite interesting on the tensile strength. In theory you could print cylinder heads, right? How lols would it be to whip up some 4AGE heads for it!
An actual radiator can be more efficient if it's painted black, but car radiators actually cool via conduction..
Anyone who claims you shouldn't change something coz "the factory spent millions on R&D you can't possibly improve on their immaculate design" etc etc are often clueless.
There are a few options for mech pumps. I think a mitsi 4M40 pump can be made to fit, Yanmar also offered a marinized variant of the 1KZ with a mechanical pump which would be a straight bolt on option and already tuned for far more grunt than the standard unit.