Actually, the only real difference between the 68 and 69 frame is the support section that runs from the base of the steering head back. If you do a search on the subject through this site you'll see a recent picture on the subject. That being said, if it were up to me I would try to source a '69 frame before I go about modifying a '68. It's just a "better safe than sorry" sort of a thing.
actually there is more to it than that
the thickness of tubing is also different (they used 3 different types of tubes ,including the last type of frame with that extra tube in)
This IS a piece of history , but as a museumpiece ,not to be used in anger
Cutting it up is wrong
People should think twice before putting wrong info on this forum , OWING a commando does not make one an expert....