If by cab you mean the truck cab roof and back window that goes on the front of a landy with canvas at the back, it's dead easy as long as you are swapping like for like. You can put a truck cab on a landy that used to be full length canvas, or that had a full length hard top, but then you will have to make some brackets for the "sticks" that hold the canvas up as the front support for a full canvas is further forward than for a half canvas. At least it was on my old IIA.
