Also just found out that the FSZE pistons are too small for the bore on the block that I have. What is the clearance between the cylinder wall and the pistons?
Do you have a stock block or did you have it overbored?
And did you mic and bore gauge them or are you just guessing?! Bore is said to be the same as both versions of engine share the FS block and have the same displacement on paper (either 82.8 or more commonly 83mm).
Skirt to wall should be about .003 -.004 or in that ballpark. The head of the piston above the rings could be a much larger gap, they're often tapered a bit.