This is my first post here. I stumbled across this topic in a web search and it caught my attention.

While I was reading this thread, I wondered if the full length die and shell plate, linked below, would fit the bill? The shell plate doesn't have a hole in the base, but that could be remedied with a drill press or lathe. Then you could use a standard press and a universal decapping die to deprime and full length size if needed with the included die. I don't see that priming with a standard hand priming tool would be that hard. Get a .25 ACP shell holder and go to town. The .25 ACP has same rim thickness as the 22lr and 0.024 rim diameter difference.

http://www.brassworldeshop.com/sharpshooterresizingdiefor22lr22longand22shortwithshellholder.aspx

My next question is, have you thought about trying Universal Clays as a powder?

I've been thinking about a project just like this. I'm thinking about using my 77/22 as a donor rifle and getting a second bolt for it to convert to centerfire. Just change bolts to switch back and forth. Maybe a Ruger American Rimfire and rework the firing pin to centerfire. Again just change the bolt to shoot the ammo you want.