Incredible work, amazing, this is much more complete than the databases we had so far based on accumulated experience.
It seems that the outcome has HUD, RADAR, but also COCKPIT functions. For example I have not been able to get "SymbolType=LOW_ALT_INDICATOR" working for the HUD. But the "INDICATOR" part is the clue for me that it is like the cockpit function "Type=LOW_ALT_WARNING_LIGHT" (that works). I am not sure.
Unfortunately, a function intended for "RADAR" does not work for "HUD" (or COCKPIT, and vice-versa). A great future outcome of the work could be to get a new "HUD" function (for example) derived from an existing "RADAR" or "COCKPIT" function (because in that case the output data is known existing from the simulation engine, so it is "just" to display it).
Some Remarks:
"HUD_" in Symbol[XX]=HUD_FUNCTION and [HUD_FUNCTION] entry is not mandatory, just practical legacy naming convention. Any name would work. Same for Radar_ (and most likely VDI_)
SymbolType=ALT_LOW_TEXT is an interesting case (not in your list). It works, the defined text will be displayed, but whatever the altitude is. A bug I guess.
BORESIGHT alone not sure, but SymbolType=BORESIGHT_CROSS works
SymbolType=CLOSURE_RATE_SCALE not sure but SymbolType=RADAR_CLOSURE_SCALE works
SymbolType=DEVIATION -> SymbolType=COURSE_DEVIATION
SymbolType=FLIGHTPATH not sure but SymbolType=FLIGHTPATH_MARKER works (I have seen your note on alias in the previous release but not tested)
G_INDICATOR not sure for HUD, but SymbolType=CURRENT_G_TEXT works
SymbolType=GLIDESLOPE -> SymbolType=ILS_GLIDESLOPE
SymbolType=LOW_ALT_INDICATOR does not work (see above)
MACH_INDICATOR not sure but SymbolType=MACH_TEXT works
MasterArm not sure but SymbolType=MASTER_ARM_TEXT confirmed yes
SymbolType=MAX_G_INDICATOR -> SymbolType=MAX_G_TEXT works
SymbolType=MODE_INDICATOR not sure, and not useful, as any function is called in a known mode so "SymbolType=" makes it (but "Type=HUD_MODE_INDIDCATOR" is valid cockpit function)
SymbolType=RADAR_ALT_INDICATOR -> SymbolType=RADAR_ALT_TEXT
SymbolType=RADAR_RANGE -> SymbolType=RADAR_RANGE_TEXT
SymbolType=RADAR_TARGET_ALT -> SymbolType=RADAR_TARGET_ALT_TEXT
SymbolType=RADAR_TARGET_ASPECT -> SymbolType=RADAR_TARGET_ASPECT_TEXT
SymbolType=RADAR_TARGET_BEARING not HUD (tbc) but SymbolType=TARGET_BEARING_TEXT works in radar display
SymbolType=RADAR_TARGET_HEADING not HUD (tbc) but SymbolType=TARGET_HEADING_TEXT works in radar display
SymbolType=RADAR_TARGET_TAS -> SymbolType=RADAR_TARGET_TAS_TEXT
SymbolType=RADAR_TARGET_VC -> SymbolType=RADAR_TARGET_VC_TEXT
SymbolType=SCALE alone I am not sure (what on the scale ?)
SymbolType=TARGET_TEXT alone ?
SymbolType=WAYPOINT_ID not ok (checked) -> SymbolType=WAYPOINT_ID_TEXT works
SymbolType=WAYPOINT_RANGE not ok (checked) -> SymbolType=WAYPOINT_RANGE_TEXT works
SymbolType=WEAPON_COUNT -> SymbolType=WEAPON_COUNT_TEXT
Again, great, very promising !