I’ll find a pic. I think .040 could be machined off safely. First 3 pics are the pistons that came in my 543 kit. 1.34 cd and a 26.7 cc dish. The next pics are the 505 pistons. 1.774 cd. I got my .040 from measuring the 543 piston thickness of the dish. The 505 pistons are .040 thicker if that make sense to u. Kim