Jack,
Yes, I don't recommend mounting a muffler this way for very long. However the camera lens distorts the size and position of the muffler somewhat, so the center of mass is not cantilevered as far as it looks. That's why I indicated this is temporary, i.e. for demonstration and testing, until I get the engine moved.
You know how it is when people come by and want to hear it start up. I've met more folks out walking their dogs, the mailman, UPS, FedEx and pizza delivery guys, even a couple of very earnest young men in starched white shirts from Utah who wanted to talk with me about the state of my soul. All took their turn cranking it over, and all left with big grins ontheir faces and thoroughly enjoyed the sound of the engine.
I'm preparing to mount the engine on a slab next to a concrete retaining wall. When I do, the muffler (and radiator/expansion tank) will mount to the wall and connect via flex pipe with a proper drip trap. However this engine is pretty smooth, so there is little whipping action.
Regarding the gaskets, yes there are a few leaks that I have to address. When I initially stripped the engine I cleaned the gaskets and smeared them with RTV, then squeegied them smooth to allow me to remove them during future teardowns. Filed the mating surfaces, too. After the gaskets dried I put it back together and have only one or two leaks that I can find. Once it gets a load on it and heats up I'm sure that will change, though.
Quinn