when it's finished, then pick it up and plonk it down.
but factories can not pick up units. Buildings can indeed pick up units, factories can not. The only way a unit can become attached to a factory is when it is being built. (in b4 zwszg)
Thus the idea to stop at 99% (unit is still attached to factory) and move that piece.
But that is limited too: if you rotate the piece around y-axis, the unit will follow as expected. If you rotate the piece around x/z-axis, the unit will not follow. Spinning makes everything cooler and if it can not spin well :/
This fugly factory can only rotate the helicopter like that because it uses MoveCtrl.SetRotation
Turn (pad, z_axis, a) would not rotate the helicopter.
(not sure if it is only because it is an aircraft but iirc was same with ground units)
pro tip
Yet another way would be to not to actually move the unit but just its pieces (or rather just its base piece of course)
Build the unit at the position you later want it to be finished but animate its pieces in a way that it looks like it is being transported there. This way you do not need gadgets.
Actually you kind of have some similiar for the"fall from sky" animation of the citadell. (sorry if spoiler)
[]Gaia_Headcrabs that ressurect Zombies from Wreckage (Megalomania i can see your walkscript errorspamin)
zK has same unit called "puppies" that eat wreackage when stand nearby and thus multiply.
The gadget is called grey_goo or so.
[]farcasterlvl2 builds unit which then cant escape the building.
select unit, press F2: is the yardmap big enough to drive out?