this is where the money comes in to it. depends how much you want to spend

You can run on std pistons and head gasket but dont be shocked when it goes bang or you melt a piston. Blacktop would be best no more than 1bar

Or you can use a decomp plate. but again would not run more than 1bar

Or a good low cost option would be to get some early C20XE forged pistons and do a 2.1 can be done for about £200-300

Or buy proper forged pistons rods ect. £700+