The best way for me to model an acf inside Planemaker, is to avoid using the background image.
When I get my reference images, I map them on 3d objects to show inside Planemaker a reference box, something that familiar to any 3d modeller, that look like that:

Make this 3d box is really easy, that will help you a lot to have a visual reference that scale and rotate with your planemaker view, but you need to be informed about some tips to do it correctly.
Let look at the Planemaker misc bodies, if your are not familiar with it, this is like working in a 3d software, with the function mirror, you model only one side, the other is mirrored
Now you can easily calculate the project dimension on the reference picture or use information taken somewhere else.
Let said we got a plane, who get 34.80 ft length, 36.7 ft span, and 12.7 ft height, now we need to modify some dimension for the misc bodies,
the length remain the same, 34.80 ft, give the misc bodie 4 numbers stations only and 5 radi/side, place the two first section at 0ft location and the two last at 34.80 ft, now we just have set up the plane length,
divide by two the span and height , 36.7 ft/2 = 18.35 ft and 12.7 ft/2 = 6.35 ft, this is because we are using a mirror object so you have to divise the dimension by two.
Here a picture showing you where to enter the dimensions (in Planemaker misc bodies panel)

Now you get your misc object, save you’re .acf, forget the error message that Planemaker give you, anyway we not going to fly.
The blender part is not too hard, simply import the .acf in a new blender scene, locate the misc bodies in the imported object, delete all other objects.
Now edit the misc bodies, and make face from the vertices, you need at least a basic three view, so one for side view, one for up view, and one for front view.
One good thing to do, is to create a new folder in our acf project folder, call it “objects” outside blender and save the blender file inside this folder with a name like 3_views.blend.
Now prepare your reference pictures, you can use one single pictures showing all your views, or split the quad in multiple face that will have a personal texture (that good when you need details, each side can have a 1024×1024px texture, even 2048×2048px)
If you are using more than one texture, duplicate your blender 3 views files, and give them some cool name like, side.blend top.blend front.blend, now open them one by one to assign the texture, and delete the non used faces (the other views, you can’t have one object with multiple texture), now export them in the objects folder, open planemaker and in the custom objects panel attribute the newly created objects
coming soon