What material for air port plugs?

Tapped the air injection ports in my 750 head and now need plugs (1/8-28 pipe). Options seem to be brass, aluminum, or steel. I'm thinking aluminum would be best to match the expansion rate of the head, but not sure. Also, what sealer material on the threads. There is going to be some heat there so need something that can deal with the heat.

Teflon tape or pipe joint compound the type made for gas in the yellow tube.
Steve

Either material will do the job equally well and use liquid thread/stud lock on the threads, Loctite etc.

i used loctite red 272. and brass plugs .that was 15 years ago .never had a problem.

Thanks for the info. Wound up buying some steel plugs off Amazon and will install them with the stud lock Threebond product I've got. No real reason for the steel plugs other than I can get them in a couple days.