you probably don't want to hear this, but there is no sense balancing an otherwise standard GX engine for street use. It simply will not make power to 7000 or 8000rpm. I wouldn't bother crack testing the rods either.

What has been done to your engine so far? I think you already have the GX head and carbs? thats a decent start. Headers and exhaust next, if you don't already have them. Then the "Three C's" - Compression, Cam and Carbs is the way to go.

I think you would be dissapointed with the results for the time, effort, and expense of removing the engine just to have the flywheel lightened and engine blanced. Those are good ideas if you are taking measures to make the engine develop power higher in the rev range, but a waste of money on a stock engine - the money could be better spent elsewhere with far greater gains - like a cam grind, compression, and carbs. Leave the balancing until you are building a serious engine.