The first time I ran into different length rods was when I was assemblyimg a NHRA legal Stocker 425 HP M.W. motor, I had used the #1 rod and piston to check all four corners and then had the block cut to get the NHRA legal spec. deck hieght. I assembled the motor and decided to check the deck hieght on all eight pistons luckily, I saw from -.017 to -.028,
.023 was the spec. deck hieght I was shootong for so I ended up calling the machine shop that I had taken all the 1963 M.W. rods I had (43 of them)and the eight pistons to build that short block to find out what had went wrong. It was the rod center to center lengths. I had
assumed he would get the center to center lengths perfect
It ended up he had no way of doing that
Never assume
I've ran into block that tapered from the front to back on one side one way and the exact opposite on the other side
I've also seen them tapered from the cam side to the motor mount side, a real beech to get the intake sealed up properly
If a man is involved making it, he will screw some of them up