First of all, I would have been lost without the help of 75Plus. Here is a summery of the advice he gave me to take on this task.
In my case, there was a slight amount of fitting required to get the new barrel to fit in the pistol frame. A small about of filing in the bottom lug of the barrel by the slide stop (as described in the Kadet kit manual) will take care of that.
The new bbl. should be a snug fit in the mortice in the slide housing so it will stay where you put it. Assuming this is so you can start with the bbl. being a bit too far toward the hammer end of the housing and bottomed out in the mortice. Now place the slide in the housing and push the bbl. forward until the slide meets the housing as seen in the picture.
This is where you want it to be flush:
(photo borrowed from another thread)
Once you let go of the slide it will back off slightly as the extractor press against the side of the chamber. Squeeze the slide forward to see that the slide face is in cintact with the chamber end of the bbl.
Carefully, so as not to change the barrel to housing relationship, move them to the vise and locate the hole exactly centered with the drill. I would start with a 3mm drill bit but just dimple the new bbl. Maybe .010 to .015". This is to ensure the hole will be centered. Change to a drill that is slightly smaller, say 2.5mm and drill through. Now go to a #32 to open up the hole some more and finally back to the 3mm bit and open the hole to size. Reinsert the roll pin and you are finished.
