Even getting Hammerspace doesn’t allow it for some reason.
Is the kit in any sort of nested inventory? Are you holding a container that has the kit in it? It might be struggling to figure out how to get the craft into your hands without clearing your hands and dropping the parts it needs by extension.
Pure speculation though.
It worked when I finally got the mechanics skill 2 through other means, is it intended to be that way? I thought its supposed to help me train to that, or is it supposed to only helpt me train to mech skill 3 then get the Simple Engines proficiency?