1527 is a beast, what esc and lipo do you plan to run?
The 1st gear you refer to is attached to a one way bearing. You should be able to slide that gear off after you remove the 2nd gear and clutch. If you allow those 4 gears to mesh after you lock the 2nd gear clutch they will not turn.
If you cannot remove the 1st gear, do not worry, just do not instal the smaller gear that drives it when you replace the input shaft for the emaxx shaft.
