Using the N13 radiator, mine has a 'some trouble' cooling. Never boils, but certainly isn't steady on 35degC+ days. It also meant that runs on the dyno would make the engine temps skyrocket.

You really must 'open up' the front panel to get as much air as possible through the radiator. Requires some reinforcement around the radiator hole to maintain the frontal strength in the radiator support panel.

I would estimate that the poor engine bay of my 1200 has twice the volume of stuff in there, and 20% more heat. There is just nowhere for the heat to go on a hot day. Putting vents in the guards via some piping from the top corner of the firewall, into the cabin and back out through to the guards would be a good modification.

I'm thinking about a dual row aluminium radiator as used on silvias etc, but a 1200 would be better off with a slightly shorter/narrower radiator though, to improve intercooler piping placement. And to retain the mounting points for the grille.