I’m an engineer as well, and outside of the torsion box that’s a very similar setup to mine. 2x4" frame, 3/4" plywood top and shelf, 4x4" legs. I have a single 2x4" runner down the middle (no torsion box, but it’s pretty quiet as-is. I could always throw more wood at it?), and my machine sits on 3/4" of foam with no leveling feet. I shimmed up the end plates to match the height of the straps, but on a 16" SO3 those don’t matter the same way. For the bucket you show in your images I actually cut a round hole in the bottom shelf to hold it so I would have clearance for my Dust Deputy and hose connections:
In same thread above look at what Jude did with his standard 16" SO3, it’s pretty slick!
Dan