My Son and I built an oversised WoodMiser cantilevered head design. It was overbuilt but it would cut 37" wide table slabs all day long.
You will have to build the mill very solidly to prevent twisting if you use a single upright post. We used 2--4" posts of 3/16 wall and the same 3/16" for most of the rest of the build, and teflon like sliders and DON'T make anything that slides without sufficient room for stuff to get in and not fall out, like bark, wood chips, etc. Our head weighed about 400 pounds and we used as much scrap metal as we could find. We used 13" trailer wheels, 12" would have been better, so our head was thicker than with pulleys, and much cheaper.
The main beam will be the strongest part to build. That is where the most overhang weight will play out. I know nothing about linear bearings, especially keeping them running free. We always washed down with a water hose every time we were done sawing. We used high quality bearings to run the carriage down the beam on inverted angle track. Cam followers would have been better, but we couldn't get them at that time.
We hung the sawhead from a 90 degree trailer winch mounted above the posts and at a balance point on the head through a pulley and back up to the winch. Used an outboard motor starter motor, modified for both directions of rotation. Balancing the head weight makes everything go easier.
If you have any questions, just ask. I'm not an engineer, but, we were successful and had minimal problems with the mill. I might be able to come up with some photos also. Good luck with your design.