One other thing...
If you change out your gears from the lower gear ratio to the higher gear ratio or visa versa, you will also need to change your bearings. The pinion for the lower gear ratio reels have a bigger inside diameter to accomodate the fatter spool spindle. As a result, you inside diameter for your bearings have to be bigger as well.
The faster gear ratio pinion has a smaller inside diameter that in turn will need a bearing with a smaller inside diameter.
The Newell 600-series use the same size ball-bearings for either gear ratios. What Franky is referring to only applies to the Newell 500-series with the 3.2:1 gears and these reels uses the same size bearings as does the 600-series. For some odd reason, Carl Newell decided that the 540, 546, and 550 in 3.2:1 needed a thicker spindle but not for reels with the 4.6:1 and 5.5:1 ratios.