I'll take some measurements tomorrow. I think it might be too light. I understand wanting to use materials you have around, however you will spend some time getting everything fabricated and you want a useful implement when you're finished. Just as well make something that will work for years and be satisfied with it's build.
I saw my first soil pulverizer in a guy's row of implements and didn't know what it was for. He explained how he used it when installing water pipe along a road right of way. When he had the job ready for seeding he'd use the pulverizer to level and smooth out the soil.