I got them out, but not without a struggle. Tamper-proof, my ass
First I tried to get a 1/16" welding rod to stick (usually the opposite of what I'm trying to do!), but ended up gouging a small pit in the plug instead. It had gotten hot enough that the temper was gone and I could drill into it with a #36 (picked that size in case I had to tap for a screw thread) deep enough for an easy-out.
For once, an easy-out actually worked. Turns out they aren't welch plugs but a piece of solid steel rod about 1/4" deep with shallow hardening.
Now I'm going to cut a small screwdriver slot in the heads of the needles with a Dremel cutoff wheel so I don't have to use an Allen wrench and hope it doesn't strip out. It's next to impossible to turn an Allen wrench with the carb on the manifold, anyway. Then it all goes back together.