Joel
You have a couple of options.
1 – Find another 6V 200mm flywheel, you can’t buy them any more I don’t think. (May be able to get a new ring gear put on yours, don’t know?)
2 - Get a 12v flywheel, a 12v starter motor, and a 12v to 6v adaptor bush, 12v starters have a smaller shaft. (This is the little bush in the gearbox casing that the starter motor shaft goes into, you always change this bush while the motor is out, they wear out regularly)
You will also have to clearance the case a little to clear the larger flywheel. This is common, just take out only what’s needed with a rotary burr, it doesn’t do any harm.
You can buy new 12v flywheels, in the US, so in Australia too :-
http://www2.cip1.com/ProductDetails.asp?ProductCode=ACC-C10-5096
Here are the available bushes :-
http://www2.cip1.com/SearchResults.asp?search=Starter+Bush&Submit=
Here is the flywheel seals :-
http://www2.cip1.com/SearchResults.asp?search=flywheel+seal&Submit=
I would use the German double lip silicone seal.
Be sure to tighten the gland nut properly, and use a torque wrench to set the clutch cover to flywheel bolt tensions correctly. Over tightening them causes clutch shudder (strange but true).
The starter you have will be 6v, they aren’t interchangeable.
Put a jack under your gearbox and take the weight to check the rear engine mounts while you're in there.
Good luck
Tony
Country Buggy King & Link Pin Overhauls, Type 1 & 2 King Pins, General Machining.
http://forums.aussieveedubbers.com/viewtopic.php?tid=74138
My car is KO813