Printrbot Simple X-axis Upgrade 296mmx227mm!

The area with the blue tape is where I can print. I need some slightly longer rods for the Y-axis to take advantage of the full bed area. The final print area I have is 296mm x 227mm x 180mm. All the parts were printed on the same printer with a 100mm x 180mm x 180mm with build volume upgrade. The only problem I have had with it is that the aluminum either is not flat, or the bed is sagging which makes it hard to level the whole bed, so printing large parts still has some issues. I am also usin