I persisted with the weeny 120Y early model standard radiator for about 6 months. The core was just about gone, so it was time for an upgrade. Of course just a replacement would not be in the spirit of the 120Y!
I'd heard that a Gemini radiator is a good substitute, it's a bit bigger and the intake/outlets are in the right place. I bought one for $15 out of the paper, and made it fit.
They go in pretty easy - I angle ground out a bigger hole in the radiator support panel, and made some little standoffs (with rubber shock mounts don't forget). Check the picture, you'll see the radiator has 'mid-mounted' plates to suit the gemini. Oh, and there are two types of Gemini radiators, a 'slide-in' type and this type. I haven't seen a slide-in one.
Well $15 doesn't get you much, it leaked slowly and had a pretty bad core. I bought a recon one for $180 (!!!) and fitted it.
Also note that the hose connection on the radiator is slightly bigger. I grabbed a random top hose (it was off a mercedes of all things) and cut it to fit. It is clamped down hard on the standard thermostat housing, and doesn't leak. The bottom hose is original, but it's really hard to force it over the bigger outlet on the radiator.
Who else out there has noticed that A12/15 water pumps can go through quite a bit before they break - and even then they just have a rooted noisy bearing, no leaks though! I grabbed a Marlows one for $30 just to finish off what now never, ever gets hot.