This set of pistons are the 2618 race alloy, not the 4032 street alloy( I probally have the alloy numbers reversed ). Diamond wanted .0065 minimum piston to wall clearances on the 4.35 bore according to the instruction sheet so .0005 more is better than .0005 less, right Not all micrometers and people measure exactly the same on the same part also , right The machine shop I used on this motors is not as Hi Po oreintated as Pettis is so we shall see how it works in the car They have a DTS engine dyno and one of my stroker bracket motors(527) made the next to the most power they have seen on that dyno Maybe I can help them get better on machining procedures, cylinder wall finishes, time between honing each cylinder and which cylinders to hone first and then in which order Win, win maybe As far as the deck hieght difference reason may be one or both I'll have to look at the original build sheet on the 512 motor that this crank was in originally with a different set of rods and pistons. I'l try and measure the stroke of each cylinder, if and when I have the heads off of this motor the next time don't we love problems BTW, I have seen varinces in motors like this with Oliver rods and Bryant cranks No perfect motors yet