@davindersangha @churchill7
Tried it. Didn't work. Just too unstable and some of the keys just didn't match up.
Next solution is to dismantle the old Atari joystick and replace the insides with joystick and controller. Need something quite small though, as the existing arcade ones seem to be a bit too big.
So, the plan is. Dismantle the joystick, have the standard single button and directional stick in the joystick, but on the controller board I would add some extra "buttons" connected to the Reset, etc. switches on the Atari machine to map with Start and Select and Back.