I've never had a tattoo, basically because I'm torn between that and accupuncture and can't make up my mind about it. So josh you're saying I ought to visit one of these places and ask to look at their titanium ..... uhhhh .....spheroids?

Well seriously, that might work for one of the Tubal Cain type small safety valves, if of the right size.
While I'm sure it's sufficient, I don't like his design as much though, because the spring (and stem) is on the boiler side of the valve, instead of the outside.
In the external spring type, the steam has a clear passage through the valve orifice and seat, the parts count is lower, the ball can rotate to even out wear, and the spring compression (and steam pressure) are somewhat adjustable, and the spring can be replaced and inspected without removing the saftety valve body from the boiler.
I suppose you could use a stem and ball running the stem and spring externally, I'm not sure what the stem would do unless you had a guide bore for the stem before the spring, and that could jam with debris.
Personally, I think a simple floating ball and external spring, is not only the easiest to build, but probably the most reliable for this small size and type of boiler. That's just my opinion.

ps. I think a proper seat for the ball is important to avoid leaks. The seat should be convex conical -- like a volcano in shape. It's true that to finally finish the seat writers generally call for tapping a ball lightly on the seat to form a very slight impression, but it may not work as well on a simple flat seat in this size valve.
You can make a cutter to from the seat easily on the lathe in drill rod/silver steel and harden and temper ( or not probably if just cutting a seat or two in brass).