I was thinking of that portable build while we were talking. It’s definitely a possibility, but the LR3 doesn’t have some of the constraints that made that build’s complexity a necessity. Gotta keep that darn cat in the bag a little while longer, though, so I don’t want to be too specific. The general idea can still be the same, but some of the parameters change for the machine mount surface.
Keep in mind that the rolling surface has to be longer than the work surface, by a little under the LR2’s current need of 11" so you’ll need to indent that ice tray into the machine area by a little.
Having the main piece like that as one unit does limit portability, I think. That piece is going to need to be a little under 5’ long and (for a 20" wide build width) … Well, less than 3’ wide. Maybe that’s not too bad, but definitely a 2-person lift. Using registration bolts for the crossmember spars would probably be adequate for making the sides parallel, but squaring would be a little sketchy, I think. I’d worry about torque on the “bottom” of the U shaped piece some. There could be an awful lot of force there, and you don’t want to make it too heavy.
I still kind of like the idea of using the truck bed as a superstructure. Each piece then only need to be about 14-18" wide and you’ll have a more or less guaranteed square and parallel pair of sides to mount the rolling machine on. The parts can be lightweight. Even if you don’t have the mounting togs that “regular” pickup trucks do, there will be something that can be done… After all, you have a CNC machine that’s capable of making whatever pieces you need to make the mounts.
I’ve already done the edits to add 50mm more Z. Unlikely that I’ll ever really need it though.
I see that diagram as having the wedges under a “tray” that sits under the ice. Maybe a double piece of 3/4" material that will support the ice and slide out of the machine once the carving is complete. If that’s the case, I might want to leave room for handholds and maybe even a lip around the ice so that it doesn’t slide off. Those are just details though.