Not enough clearance between cylinder head and front wheel on full compression unless it was mounted at such an angle to the airflow that the rad would become, to all intent and purpose, a solid wall with no air flow through it.
I'll probably get the custom rad built along the lines of a Ducati race rad with a section that clears the front cylinder head...
The roller itself is an off the shelf product sold for dirt and road bikes, it's made from a hard rubber/nylon compound of some kind. How long it will last I'm not sure - Crescent Suzuki had a similar roller fitted to the BSB machines in the John Reynolds/Yukio Kagayama era and a roller lasted pretty much a whole season from what I remember...