I got my belt today for the rotary, so was able to mock up the bed. the first layout was to support the rails on the very outside cross beams.
This looked ok, but once I got the height I wanted and added the 6" chuck, I was losing about 4" of workable space on the spindle.
My rails are the same length as my machine, so the next option was to cantilever the tail stock end over the next to last cross member. This actually looks to be a better option as if a heavy piece was on the rotary, there may have been some flex in the bed rails with no support in the mid section. The tail stock is also a couple of inches shorter than the head stock, so I'll have a just enough room to slide in a section of bed over it should I need the wider space.
This put the chuck completely outside of the working area of the gantry by about 1/4". It also allows me some room to mount the motor below the head stock. I'll have the maximum amount of working area, which is 48" with some room for the center on the tail stock end.
My other project is the dust boot re-design. I 3d printed this piece, which was scaled to fit my shop vac hose.
Rather than sucking the dust from the side of the spindle
I'll enlarge the hole in the top of the printed piece to allow more pass-through of the spindle shaft and collect it at that area. My boot will be re-cut to use some 3" brush in an 8" diameter around the spindle, which should give a bit more flexibility to the brush and they will be far enough away from the bits to keep them from being in the way.