This has been done time and time again in Finland. Because of the shape of the XR3i pistons, 1mm doesn't do much. If you take the entire dome away, you will have a piston that is exactly the shape and size as a RST piston. It will take 200hv, but certainly not as lightly as RST pistons which have been done with a different casting process.
The turbo oil feed and return is best and easiest done exactly like in a RST.