You need to install first EEAH then EECH in merged mode (both in the same folder). Note that if you use Galaxy, it not allow to install the two games in the same folder.
I do have both installed in the same folder, but I still have that problem. It says "Apache vs Hokum: Installed" in the top right corner when the game starts. I noticed that the problem also appears on the KA-50 and also the Hind I think.
What is "Galaxy"?
Galaxy is the game client of GOG, such Steam and Origin, only that is fully optional.
About the gauges, if both games are installed, it's supossed that their need to work. You run EEAH at least once first?
You can try to install the latests mod for SimHQ, but be advised, the current modding team are purism fanatics, so if your like the original gameplay, you are to be disappointed, because the latest mods are oriented to make te game more realistic (and complex and boring) instead of a good balance between realism and fun.