Here are 2 versions of the 10" Y-bed in DXF format that could be used for aluminum cutting & also 2 versions of my guess for the 12" Y-bed. This has the hole patterns that work for my 10" Y-bed. 248.6mm between centers of Heatbed mounting holes.
209.38mm between outside aluminum extrusions
228.38mm between Wheel holes along the X-axis
I also need 2 dimensions to set the Limit switch hole.
I assume the limit switch is done similar between the 10" & 12". Y-Bed_i3v10_AluminumFrame_rev39.dxfY-Bed_i3v10_AluminumFrame_rev41.dxf

If you can verify these dimensions or give me the correct ones, I will design a 12" plate based on my 10" design.
I also attached 2 versions scaled up by 1.2 as my guess for the 12" plate.
Y-Bed_i3v12_AluminumFrame_rev39.dxfY-Bed_i3v12_AluminumFrame_rev41.dxf