While I haven't added anything to the large array of P-51's out there for fsX, I do routinely use this set up for several birds. It has colored flames plus a bit of smoke. your will have to play with the coordinates but it does produce cool visuals.
//------------ ExhaustFlames--------#2=strobe to control, but I preferNav lights
//index,type, long, lat, vert, fx_filename
light.11= 3, -20.100, 11.10, -3.90, fx_V12_IDLE_starb,
light.12= 3, -20.100, 11.10, -3.90, fx_V12_MAX_starb,
light.13= 3, -20.100, 11.30, -3.90, fx_V12_Exhaust,
light.14= 3, -20.100, -11.10, -3.90, fx_V12_IDLE_starb,
light.15= 3, -20.100, -11.10, -3.90, fx_V12_MAX_starb,
light.16= 3, -20.100, -11.10, -3.90, fx_V12_Exhaust,
In case ya don't have the effects, here they are.
View attachment 67948