I always rated the iron Polini kit. It is good to see that they have adopted a 2 ring piston for this kit but the ali exhaust stub of this design has proven to be a problem. If the exhaust comes loose, but remains undetected, the stub can wear to an extent that cannot be rectified easily.
I wonder if the two ring piston will fit the iron barrel? I've got one sitting in the drawer in the workshop that could do with a piston.
BTW, Harry Barlow is having a copy of this barrel made in India, with the intention of making a bolt-on torquey tourer for the P2 lump.