Both of my Italian .45s are GS series engines. I have been trying to get my hands on an S45 ABC piston and liner myself to make my S45 more appealing to sell. The S series engines are timed lower than the GS series engines - one of the primary changes they made when they discontinued the S series and came out with the G series. Some engines got more than a cosmetic exterior makeover. S series piston/liner sets do not fit GS series engines. The OD of the liners are completely different.