I think it would be a total pain in the ass that wouldn't be worth doing. The thought of installing a 1.6TD into an ALH chassis just makes me cringe.
A small hurdle would be replacing the pedal potentiometer and adding an accelerator cable. I think that a bigger hurdle would be getting any gauges working, all of which run through the ECU. Unless your time is not worth anything at all, you'd probably be better off just selling the 1.6TD and if you happen to need another running vehicle while working on your ALH ride, then get a SECOND ALH. If you keep up on the basics, the ALH is bombproof and probably the most robust engine VW has made. The ALH vehicles are also at the very bottom of the value curve so it is a good time to pick them up.