I also have had a idea to make use of some more of my HO scrapbox for some time.
The CPH needs a mech. Take one Athearn SD mech in said scrapbox, a set of Slaters rolling stock wheels, remove HO wheels, cut back steel bearing mounts on at least one side of bogies to prevent shorts, take out the gears at each end and drill out to 1/8" , insert O gauge wheels, add pickups , make and mount new sideframes and voila.
The photo above shows the drive bogies before addition of pickups and sideframes. Photo of that stage to come later.
The wheelbase is 6'9" instead of 6'6" but I won't complain for the price.
Another set might make a 79 class mech which is 6'10" w/b.
More has been done to the 18 class and photo's to come when the couplers have been added.
I have also tarted up an Atlas F9 to vaguely look like a 42 class. I have had the model for about 18 years and have failed to find a satisfactory use for the mechanism. It has been languishing in Mount Newman colours for some time.