Ok, I bought the radiator today at AutoZone. It's a Spectra Premium #CU1494, for $94.99. RockAuto sells it for less, but I just didn't want to take a chance on shipping damage or delay.
It looks like an exact copy of the original, at least along the top. It's plastic/aluminum. I will have to install the ATF fittings at the bottom. These are just flare connections, which I hope won't leak.
The remaining issue is the coolant. I determined that the shop which did the 60,000 mile service did not use Honda coolant. They say they use top quality non-silicate, non-borate coolant, but they consider all such products to be essentially the same, and their source varies from time to time. But they don't typically use Honda coolant because of the price.
If I could match what they used, I would refill with the same thing. But it could be Prestone or Xerex or whatever. All I know is that it's green. I have about 1/2 gallon of Honda coolant that's green, but it's quite old.
So the best I can do now is refill with new Honda HG coolant
- the blue stuff. If I though I could get to it and remove the block drain plug, I would do that too, but I think it's unlikely that plug has ever been removed, and I think any attempt I would make would likely be unsuccessful, and possibly damaging either to me or to the engine. Of the three shops I talked to about doing the radiator for me, none of them, including the dealer, said they typically drain the block when doing this job.
So I'm going to end up with a mix - mostly new, but some old - and just hope they don't react with each other in some way.
I appreciate everyone's help on this. I'll be into this for about $140 versus at least $400 for the shop to do it. I confirmed that I can with some difficulty get to the lower hose clamp at the thermostat, which was the thing I was most worried about, so I should be able to do this without major complications. I hope.