Ben,
I think it needs some more fine-tuning.
The illustration shows that the bracket and the rubber isolator are all jammed together with no gaps to allow the radiator to move. That's really not much different than having the whole thing made out of steel.
The main thing you want to do is constrain the radiator from moving front-to-back (toward the firewall or toward the grille), so brackets that creates a vertical channel on either side would accomplish that. To secure the radiator from lifting up and out of the radiator support, I would focus on a rubber mount across the top somehow....think short "bungee-cord" type straps from the radiator support, across the top of the radiator to a bracket on the fan-shroud side. This will allow the radiator to move upwards (slightly) when the frame is flexing and won't transfer those forces into the radiator itself....the radiator will simply push up against those rubber straps and deflect them as it creates the clearance it needs.
I envision a set of brackets that are more side-mounted on the radiator, with rubber straps running across the top...
ps. This advice is worth what you paid, and the more people you ask the more opinions you'll get.