Regarding the missing cross/fuselage fuel tank on "Sierra Sue II" - it did have the fuselage fuel tank (all production P-51D's did) and cross marking, but when the female bust was painted on the side of the fuselage, the data block and cross were removed.
Regarding "PBR", it's the plan going forward for all future releases (PBR workflow for FSX and P3D and PBR materials for P3D). With the B-25J, as to the textures, I'm still in the bucking rivets stage, adding screws, etc. (each rivet, spot weld, screw, and fastener individually placed directly to the blueprints, accurate to production block). A P-51A/A-36A/Mustang Mk.1/F-6A series has indeed been in the plans - I had started on it at one point, but I have a lot more to go on now, including the ordinates (like I modeled the B-25J to - accurate at all points to a thousandth of an inch), so I would be inclined to begin again with a clean slate. This would then lead well into developing a new line of P-51B's/C's as well.