I did it with my Kirby G5
When it came to me about a year ago, my G5 needed a lot of love. The back part of the handle had been replaced with one from a G4, which is fairly common as something in the G5's burgundy pigments makes the lower cord hook more fragile than other colors. The brush roll was shot so I replaced it with a new Sentria style one and the cloth bag had holes in it so I found an entire bag assembly from an Ultimate G to replace it. For aesthetic purposes, I put the burgundy bag topper back on it, which helps bring out the flecks of burgundy in the otherwise mostly gray bag fabric, thus complementing the G5's unique color scheme. I have occasionally considered taking the color integration further by putting the original burgundy emptor on as well but it seems like a lot of work for no functional gain, especially when the light gray one is in much better shape. From a functional standpoint, I do prefer the newer style outer bag with its curved zipper.
So all told, my G5 is made up of fully compatible parts from four different Kirby models, all of which have made vast improvements over its previous semi-decrepit condition and in some ways may even arguably improve on the G5's original design.