BRN12345

I am currently building a road race transmission and have changed my 3rd and 4th gears to shorter ratios (1.636,1.31) and I was planning on swapping my current 4th 1.034 into 5th gear position. Upon disassembly I found that the 4th and 5th gears are not similar in height (fourth gear has a longer sleeve) and that they wont interchange. I then went and tried to see if anyone makes a shorter 5th for the H22 gearbox and couldn't find any. I am now thinking of machining the 4th gear to replicate the 5th gear dimensions. Has anyone done this and if so what needs to be done.