Hi - You are assuming that two separate beams share a load equally in this arrangement, they do not. Plus the bearings are rigid and they do not allow a twinned set of bearings to load share either. You will have to figure this out for yourself I suppose. Read prior post with mind experiment in it. If you take the web out of an I beam it does not hold up the house, that is what you are doing. The bearings are not a connection in the sense of being able to transfer moments and shear across the gap its a "rigid" bearing so can only transfer the direct load due to the deflection of the lead beam which is tiny.
Peter
Plus to be equal to the HAAS you are going to need 800kgf at the tool which your bearings are mounted on thin pieces of metal which will deflect. Lots of work to do... The HAAS requires a crane as well...
I'm sure a sponsor will get you the material if you ask around, plate aluminium is the go easy to machine and light... design the machine and the material will come, stay away from welding.