The wg 3 was one that came up in searches. I guess drilling and adding will be the best thing. I would rather send it to someone who has done some instead of trying it myself. If I didn't cut at such different elevations I would just ream the jet out. I don't think it would run very good at 4000ft when tuned good at 1000ft.
I've done the WG3 swap before, you have to swap the throttle shaft since the WG3 isn't setup for
the throttle cable the 3120 uses. And you have to still drill and tap the carb to to move the idle screw.
You still have to swap the fuel pump side plates since the WG3 uses a pulse hose, then you have to
drill the carb body to get pulse. And the 3120 gets the pulse through the intake manifold.
It's just flat out easier to send it to Eric, Simon, or who ever and pay them to do it.