The owner's son told me with some degree of pride that he figured this out by trial and error.
Mostly error from the looks of it.
Pic 1 The panel is fed from a 100 amp panel on the right.
Pic 2 A mobile home electric furnace on an OSB box he built.
Pic 3 My reaction. I refused to touch any of the equipment. In order to run the 4-0 SE cable he'd scavanged he cut strands off of it until it would fit under the lugs on what ever breakers he salvaged.