It's certainly an interesting display engine.
The base tank (part no #A-32-26) with no mounting tabs was made for at least one tool, the Orline Yard-Arm, but that doesn't use a gearbox as it's direct drive, is it possible it's been added to display the engine?
The blanked off PTO shaft is used when the shaft is fitted to the other side of the gearbox, i.e. towards the engine, the chainsaws & bicycle engine kits are set up like this.
That style of muffler/exhaust is used on some of the chainsaws, such as the Model 13 Mustang.
Has it got a engine model/type stamped into the cylinder baffle plate or on the end of the crankcase mounting flange (exhaust side)?
David