A Chinese company called GPI Racing offers replacement radiators for many vehicle applications, including the RC24/26. They're prevalent on eBay under several names and sellers, but I suspect they're all made by GPI. While appreciating the economies of large-scale production, I still can't help but have healthy skepticism of a $75 (shipped) item that Honda would certainly price at many hundreds of dollars.
I was unable to find much firsthand experience on the usual internet forums, so decided to find out for myself and ordered one. Arriving in less than a week, I was first impressed by the packaging, and then by the look and feel of the product itself. The radiator appears robustly made with quality material, nicely finished welds and cap included. Some of the mounting tabs are a bit crudely cut and not perfectly aligned but, again, very robust.
(click on an image to enlarge)
The OEM temperature sensor screwed right in place; I will replace the sealing o-ring, still available from Honda.
The Gen 2 radiators were supplied with two types of grill mounts; one had the upper two mounts using a tab & slot mounting with the lowers using screws. The other style uses screws top & bottom, as does this new radiator. My issue is that the screw mounts are not threaded and too thick to use the original U-clip screws on top. After considering different solutions, I settled on well nuts (below). I drilled out the existing mounting holes to fit the well nuts and tightened the screen in place. One of the four mounting holes was about 2mm off-center, but a little filing had everything lining up.
The only other nit is that the coolant overflow hose fitting is larger than OEM so I'll need to address that, probably by switching to a silicone hose which will tolerate stretching over the larger fitting.
l'm in the early stages of this build so the radiator will be coming off for grill refinishing, engine detailing and silicone hoses fitted.
Final thoughts: I'm actually impressed with this product and pleased that there's an aftermarket radiator available for the RC24/26. I half expected quality and fitment issues but found nothing of note. The manufacturer claims better cooling and TIG welded aluminum in a "vacuum brazing furnace" (above my pay grade). I plan to make use of this radiator long-term on this project, fully realizing it's an unknown quantity, but then so is a tattered 40-year old original.
VFRworld forum member Fastdruid added that his installation required lots of fettling to fit. As for longevity, he's been using it for two years problem free, including two track days.