I would check with Mikael at RPM Mustangs.com, I know that he sells some kind of pistons for overbore etc. Dont' think it matters how much overbore as far as price, but I would ask the "man" make sure.
Rick Kilpatrick, AAS Automotive Systems Tech, Alamance Community College, Class of 99. 06 5 speed manual Mustang with Pony pkg : GT Mac Mufflers, true duals with one custom pipe. 2.5" system. GT bumper cover, all installed March 7&8 2006. AFE Stage 1 CAI, Motoblue Underdrive pulley, GT aluminum shifter knob, honeycomb rear blackout panel,and dash kit installed. Roush hood scoop and side window louvers installed. SS taillight trim has been installed, new alum. GT steering wheel installed.