I have 2 stands and one is exactly like you describe with about a 10 or 12 inch wide "axle" at the front end. I built my 250 on it and tore down 2 others with no problems. It does help to have somebody steady the engine while torquing down mains and the head so you don't have to chase it all over the garage. It has never given a hint of falling over.
You could use a piece of square tubing 30 or so inches wide on top of the front "axle" and drill through it and the axle to bolt it to form a sort of outrigger if you're worried it may tip. Another small length welded or bolted to each of the ends of it to be near the floor and forming an upside down extended U could also be done. When you don't need the outrigger just unbolt it.
