Well actually what is weird is those 2 sachs kits that are out there actually have the same displacement. Like 78 or something on a 505 1d.
The "bigger" one just has reed valve induction.
Is your engine a 505 1d?
First things first. Get a carb and a pipe.
Personally if I were going to spend big bucks on a G3 (and I am going to be) I would look on nazibay or ebay.nl for a sachs 505 3dk or 505 3dx. Either one will solve your clutch issues and be fast since they are 3 speed manual engines. Totally bad ass. I have been eyeing them up for a a grip now. The hardest part is getting one of those people to ship to America. for some reason a lot of stuff on euro ebays is pick up only, even if its just like a pipe or a rim. Its dumb.