You might want to check out www.teamtrinity.com as I think that they are the US distributor of Picco car and truck engines.
I picked up a spare head in very good shape cheap for one of my air-cooled engines to experiment with. You'll find that the car and truck racers seem to like the larger aftermarket heat sinks or will replace one if it gets damaged from too many roll-overs. This way you have a good one and other to hack on.