Well done with your efforts so far.
It is only now that you can start to appreciate just how simple these little motors really are and why they corrode so much in certain areas!
A little bit of correctly applied maintenance once in a while will go a long way with these.
HEAT (and sometimes lots of it) will be your best buddy when stripping down an old engine like this.
Gearboxes dont usually give much trouble when stripping down, except perhaps the drive pinion, or a stubborn screw.
Dont be scared to heat the aluminium gearbox casing quite a lot to help "expand" the metal enough to drift out the pinion.
Arm yourself with a decent plumbers type blowtorch and some solid steel bar to act as a drift to push out the pinion.
Word to the wise here, before you start removing the pinion check to see how much play there actually is in the pinion! If it's still acceptable, then leave it alone. (it might just cause you more problems later on)
I often find that trying to seperate a gearbox from the pumphousing gives rise to a lot of cursing and swearing!
Once again, heat is your best buddy, although go carefully if your motor has an aluminium exhaust tube fitted.(dont want to melt that)
A gentle rock from side to side (sometimes twisting) while everything is still hot is normally enough to get things moving.
Only use a rubber hammer as a last resort.
Stick with it and you'll get there.
Help always on hand, just ask.
jon
Very happy with that.