Thanks Jagd, but I know about the Donationware - I've even done a couple of skins for it available here at SOH. But it is not openware like the Alphasim version. Any further development other than skins is severely restricted.
The problem for me is that I have started the development of a new campaign which dependent exclusively on the P-51B and P-51D. The FDG P-51s don't have the performance to work in the missions
While the Donationware P-51B and P-51D are great models, unfortunately they don't have the top airspeeds, the operational range and other handling characteristics of the real aircraft. I don't mean any criticism to FDG2. They fly well enough, they just don't meet the operational and performance parameters of the real planes.
In fact, none of the free CFS2 Mustang models available - including the much favored Wai version - have accurate performance modeling. I've spent the last couple of weeks testing every model I can find, so I know now. I haven't tried any payware models but that's beyond the scope of anything to be used in a free campaign anyway.
That leaves me to build brand new P-51B & P-51D flight models - air and aircraft cfg. files.
I have just finished doing a new flight model for the Alphasim P-51D, along with a new accurate panel and other tweaks. It will now reach the published top speeds and range, while maintaining the climb, turn and dive characteristics of the real P-51D. I would have liked to do the same for the P-51B.
If the Donationware P-51B is the only viable P-51B model, then I'll need to ask for permission to fool with it.