From the drawings we showed you in the December issue ("Fun Buggy Blueprints," page 128), you can see the sheetmetal-fabricated lower substructure within which the transmission and transfer case reside. Additionally the link suspension also ties into this subframe. I rounded up a few sheets of thin 0.090 and 0.080 chromoly sheetmetal to build the substructure with from CalTime Metals. The chromoly is inherently stronger than mild steel, and can be heat-treated to make it very resistant to deformation and abuse. However care should be taken when welding chromoly and it is quite a bit more expensive than mild steel.