Hi Bill. Raining in Ruidoso now. There was an outfit making the tail housing casting (only) but I notice nobody seems to have them in stock any longer. Not a good sign today. You can do what I ended up doing, however: https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1305319/1.html
You'll see I created 2 different electronic speedometers and ended up choosing the simple one. If you want to make it even simpler than mine, you could use the SpeedHut GPS speedo mechanism. I discussed this with them a few months ago and they assured me it would fit just like the one I used. Let me know if you need the image files for the speedo and gauge faces.
Or you could use one of the pulse-to-mechanical adapters, but I haven't seen anything to make me want one of those.