I just finished a Standard 2448. I made the base out of 2x4's. Honestly, I got it as close as possible with lumber and planned to shim it for level. Turns out, I didn't need to. The machine was so rigid that it held its own. I worried and fretted and such for a while, but it worked out without any fuss. I did flatten the spillboard after everything was done. So far, everything is working pertty well. Let me qaulify that by pointing out that I have not fully utilized the full range. Once I get out there at 48", I might see something different!
Enjoy the new toy!
Tony