A real pain
Ed,
As pointed out, I did this ten years ago. I cut the spinner down to the point that the stock backing plate fit the spinner, about 1 inch if I remember correctly. It was then necessary to fit the forward bulkhead, moving it forward on the prop with about 1" worth of spacers. This required some careful measuring to drill to fit.
The problem is that even though the back plate "fit", the flange does not have the same angle as the spinner so there is a slight gap. After about 700 hours a crack developed around the prop opening at the prop opening. I attribute this to the fact that the spinner does not fit flush to the flange. A small weld on the spinner lasted another 100 hours or so.
I am now working on my second fiberglass spinner that I molded from the aluminum one (not happy with the first). Unfortunately, my mold broke in the process so I will not be making any more.
If you are good with glass there is another option. Tom Clark used the same prop and spinner but performed major surgery to the cowl and got a great fit.
Or, go with the MT.
Scott