i bought a new radiator when i swapped my h22a1 because i didnt want any contamination to the new block.
i rebuilt the motor with all new parts, so a mildly used and corroded radiator could ruin my brand new water pump and begin eating away at the inner block passsages, etc.
u get the idea

the two radiators are different but since the radiator is already very overefficient at cooling the engine (at least on hondas) i dont think its an issue.

yes the h22a1 and h23a1 use the same ECT sensor for the gauge

however the ECT thermo switches (mainly ecu load data and fan operation) are different between the 2 motors

~boom