They will supply the rings but I don't have the specs for the rings yet.
I can send them SR42 piston as a sample. SR42 has the same stroke as SR43 but still has completely flat top piston like SR41. I think there was some difference in camshaft of SR43, have to check. For sure there's a reason for recesses in the piston of SR43.
I have spoken to 3 companies - JE, Ross, and BRC pistons. They have all given the same price range.
It is still in the planning stadium. I don't have the funds to buy 4 pistons for myself so if there will be not enough interest I will go for plan B