Unless you have a lot of scratch building experience, you are better off staying with the "D" model. The "A" & "C" had shorter vertical stablizers and they did not have the trailing edge filet that the "D" model had. These two problems would not be too hard to fix, but the speed brake and speed brake well would be. The "D" had a larger well and speed brakes and the brakes were shaped much different.
Berny
Phormer Phantom Phixer
On the bench
TF-102A Delta Dagger, 32nd FIS, 54-1370, 1/48 scale. Monogram Pro Modeler with C&H conversion.
Revell F-4E Phantom II 33rd TFW, 58th TFS, 69-260, 1/32 scale.
Tamiya F-4D Phantom II, 13th TFS, 66-8711, 1/32 scale. F-4 Phantom Group Build.