No pic - haven't built any yet, but the most common thickness is 10 gauge 2 x 2 steel. You do know you'll have to fab from scratch. I would not be able to supply a pic because I'd fab them basically in place and the way I route mine might not work for your equipment.
Yeah. The 2x3 box drops right into the factory frame rails from above and overlaps by about 1/2". Weld it up and it's done. Total material cost was about $10.00, 3 - 4 hours cutting, fitting & welding.