What a project but I would rather be working on the bike. I hope nobody buggers up their gasket surface with this idea or the pushrod tube press. That was pretty funny.
You should use the tool a bit and see if it works. It surely won't as photoed. The flat bars will hit the head. The funniest thing is I can't figure out what keeps the valve from going down too? The whole point is to keep the valve in one place while the cap gets pushed down?