I have some pictures here may help with the gearing issue with the Abu Garcia 6.3 and 5.3 main and pinion, gears..
The first picture, shows both the 6 and 5.3 gear sets,, Notice the different profile of the pinion teeth..
The next few pics show the measurements of the main and pinion teeth diameter, they're different..
The final picture,, shows, a bit unclearly, you have to look close... the different pitch of the teeth on the main gears.
Each of these parts has a different part number, and, they won't interchange successfully unless they're matched. Ratio to ratio.