Like Erik stated it isn't the bore. LS1 and LS6 blocks have shorter sleeves than LS2, LS3, LQ4/9, etc. blocks. If you pull the piston too far out of the sleeve it will cause oil consumption issues, and in some cases the piston will rock at the bottom of the cylinder causing excessive premature wear. While I would trust Erik (and probably only Erik ) to build one, I certainly wouldn't try it myself or take it to just anyone.