I double checked to see if my statement was correct. I got confused about what fits and what doesn't (I have a lot of Zowie mice and I have messed with them a lot). My original statement saying you need to modify something is wrong. Sorry. My memory got mixed up with the lens fitting with the different sensors/PCBs rather than fitting the bottom shell.
The ZA13's 3310 PCB, wheel, cable and lens will fit into the 3090 yellow and black FK without modification. I put my ZA13 internals into my yellow and black FK to verify.
The yellow and black FK internals can fit in the ZA13, however, it appears that lens doesn't perfectly fit the bottom shell. When you put the PCB in, with the lens, the PCB does not lay perfectly flat, it will bend slightly when you screw it down. It looks like the prism area is what causes this. It's not necessary to modify anything for it to fit, but I am not sure if it will cause any tracking issues.
Edited by popups - 7/20/16 at 12:10pm