I brought my too short fork to a metal fabrication shop that mostly deals in pipe works.
For their minimum shop price of $120 they put an inner sleeve in the steerer and welded a piece of a donor steerer on. It worked well.
I think it added something like 80gm to the fork.
Otherwise, those extensions should work. If you do, use a real bolt, not a Philips head. You’ll want some locktite on the threads. I might even put green locktite on the mating surface. Remember, this thing is basically keeping you alive and will almost be unserviceable once installed.