#54592 is the number for the tb04 specific spool, that has 40t ring gear
If your going to change the gear to 39t, might as well get the tb03 spool diff and use shims to make up the space. You can purchase the tb03 gears seperately too #51255
You can achieve an fdr of 2.29 by using #51109 (17t/39t), you will have to remove the lip on the bevel gear so you can fit the e-clip