I'm going to say no. It does rid the surface of casting flaws and allows the gasket to sit and seal superior to leaving it. The stuffer backplate is much wider than the stock backplate taking up the case in it's entirety. A few in our club have made backplate from Delrin for the Fox.35 and they have noted that the overall depth can also be slightly increased.

       Does removing material effectively stuffer-backplate-ize a Fox 35?

   No, and unless you are running it in racing events, you probably don't need to do anything to the backplate. It is intended for durability, and not to change the performance. It is extremely ambiguous whether reducing the crankcase volume has any beneficial effects on any of these engines.

  It was invented (by the late Marvin Denny) to keep the conrod from being pushed backwards and thus wearing out in Foxberg racing events. Whether you need it or not probably depends on how close the cylinder axis is to perpendicular with the crankshaft. It varies from case to case,  apparently to a significant degree.

    Brett