Sorry for the late reply.
"Attaching" a sound is really easy actually, but I use a different mission building program... Is that simple as this : next action after random choice action, should be a "say" or "play single sound action"... ie connected (referenced) to random action.

About P-51, I use the "classic" method for planes lacking a modeled HUD glass :
- Assign a button at FSX Controls for screen centering
- When time comes to this, hit that button & "light up hud" (Shift + 3, by default)
2D CS HUD is centered at screen center, which centers with pilots view as it must be...