I started with a 1981 early style motomag frame , made some measurements and it was good to go.
The most important thing for my was to get the geometry as near to the standard frame but wider.
I have now sold a lot of the parts for this build and In the process of turning it into 1979 Team spec, I am waiting for the mongoose double clamp stem to come back from the finishers and then building will start on the new improved look.
Here are some of the parts I have to fit.
Nice fab work! sweet build. mine is not nearly as cool as yours but my wife and daughters found this while Christmas shopping last year and got it for me...