No one is smoking anything.

Looking at the jetta.golf manual the specs/gear ratios are laid out.  They are identical for the 1.6 desiel and 1.8 gasoline. In print. The difference appears to be the torque converter which you will not use.

There is not question that the body and internal parts are the same. This is confirmed by both john of main, as well a proffessional rebuilder of transmission.

I don't see any pictures or other information in the bently manual which suggest that the desiel tranny is "different" than the gas one.  As so, it is very good thought.