MPG Motor Magnum vs. Hemi

You could connect the 2 tanks with a lower feed and upper vent line so you can use and fill them together at the same time.
As the stock tank is upright and probably higher than your 2nd tank, it will always properly flow into the 2nd tank with the fuelpump.

A guy running Imperial Services used to make/provide conversion cables to hook a later style transmission to stock pushbutton controls.
One of the mods was to replace the detent spring with a weaker one, as the lever on the transmission is very short, because the throw of the pushbuttons is short too.

There was speak of him not wanting to deal directly with buyers anymore so he might sell his items through a dealer. But I'm not sure if he still does this.
His prices were very firm btw.