I missed this thread last month, but given the age of vehicle, and the uncertain history of coolant changes (probably never), I've been thinking clogged radiator all along. Now that you know you need a new one anyway, replace it.
You don't need to spring for the Honda OEM part--a good replacement brand will work fine at ~half the cost. Modine is a brand I've used a couple times without issue. Make sure it's new or "re-cored," and has a warranty. Do not buy a used radiator, no matter how tempting the price.