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Or just machine a piece of pipe to go between the dome and the safety valve if you want them to sit up higher. That's the easiest thing, and you can make it a bit longer and then cut it down to get the exact height you are looking for.
On my A3 I actually made a traditional steam dome which Kozo did not do for the A3 because the throttle assembly is brought out onto the top of the rear boiler barrel. My A3 is 1.5" scale so I have a traditional steam dome throttle. Because of that, I fabricated a real dome which gave me the ability to push the safeties higher up in the dome itself. The other suggestions work as well. You could lift them up on pipe nipples or whatever.