I've started to model the 3rd concept and I'm already worrying about the build area. With the overal height of 710mm, I'm just about able to squeeze out 330mm of Z height. This is while reducing the allowed cartridge spacing height from 70 to 60mm. 

I'm probably going to either move the HGR Z axis rail or switch to 2 MGN rails so that the ballscrew has somewhere to go. The roller is connected to 2 Nema17's on each side which are 20mm in lengtth. I still have to figure out where to put the roller linear rails. I've also got concerns as to how much resin the cartridges will be able to hold, and might have to go back to the 4-screen (356mm) build volume. Pricewise, it doesn't make an impactful difference, but I'm still constrained in footprint space.

I'm expecting the LCD + UV assembly to be 200mm in height. I've also added 2 white LEDs in the ceiling for lighting when printing is finished.