Dan, that's quite the robust tailstock you've got there. Can you rotate the chuck or is it fixed? If you don't mind my asking, what is it that you're doing in that first photo-pillow block and spider as a steady rest-all very interesting? The second photo with the router also is an interesting set-up. I see you're using it as a duplicator with the router sliding in and out on a track (similar to the sliding of the yoke on a radial arm saw). Care to comment on that as well? Is there a template in the background for controlling the router cut?
The SuperShop, as well as Shopsmiths, are so adaptable to custom set-ups in the right hands. Nevertheless, they get a lot of criticism, most of which stems from the saw function of these machines. Their versatility is surely overlooked by many.
STnewman, I'm curious regarding your plans for metalworking on the Supershop. A 4-Jaw independent chuck is more versatile than a 3-Jaw scroll chuck as it will accept more than just round stock. Iit's more accurate as well, but take more time to set up properly.
I've got a 6" 3-Jaw and 10" faceplate that mount to my Smithy which has a 2 1/4" x 8 TPI spindle. Unfortunately, the don't fit the Fox's 2" x 4 TPI Acme spindle. I rarely use them as they're overkill for most woodworking. I can also mount my Nova woodworking chuck using my homemade Shopsmith adapter.
I also have 5" 3-jaw and a 6" 4-jaw from Grizzly that fit a 1" x 8 TPI wood lathe spindle that I could mount to either the Fox or Smithy with an appropriate adapter.
Stnewman, I only added all of this regarding these chucks as there may be other options depending on what you're planning, rather than having a custom backplate made in a machine shop. Although, a chuck mounted to the spindle threads is the strongest and most accurate option.