Stock radiators can & do plug up over time and this will reduce the cooling efficiency.
Get an OEM replacement from Modine or Rock Auto.

FWIW I run a stock OEM radiator on my H-prod Civic with 11:1 compression and and spin it up to 7500 and I have no problems with coolant temps. In fact I have to run a T-stat as we found I would lose power if it ran too cold.

I run plain water + water wetter.

Make sure the head & block are flat & true.

Don't know if you are running one or not but ditch the Honda oil-to-water heat exchanger and run a remote oil cooler.

Are the dowel pins for the head in good shape? I use new ones everytime I pull the head. Cheap insurance.