First let me address the OP's original question about Cardboard cutouts for various fin and shaped models:
Yes it works well with ANY shape model regardless of fin number or wierd body configuration. The trick is to do Two Views. Top and Side or Bottom and Side whichever give the best representation of the vehicle configuration. Balance both to get the LCP for each view then average the two to get the LCP location for the model. from there simply measure forward ONE Caliber (largest Body Diameter) to locate you vehicles CG. Now add weight the nose to move it to that point on the completed model. After doing the cardboard cutout CP-CG method I Swing Test the model to ensure first flight stablilty. Even on Larger models and MPR's. Try to swing the model starting with the nose down about 5deg.
If your having trouble tracing the model outline it can be done with photos as long as they are taken from exactly the same distance. This way you'll get True Scale cutouts that can then be balanced and meauresed then scaled up to the full size model. Takes a bit more time and math doing it this way but it Works.
The other tracing method is to suspend the model over your cardboard with a very bright light directly above the model. Trace the darkest outline shadow on the cardboard. Hang sideways and repeat to get the side view without moving the distance between model and cardboard. On larger models I do this with the cardboard or paper on the floor with the model suspended on two strings from a gooseneck floor lamp
There is yet another way that I haven't seen anyone bother to suggest.
Back in the Stone AGE BC (Before Computers) Home PC's anyway. We had to find our model CP's the old fashioned way...with Pencil, paper and OMG a Slide-rule!
Then in the very early 1970's Centuri put out a series of Technical Information Reports TIR's that made these calculations Much Simpler.
One of which was
"Calculating Model Rocket Center of Pressure". This phamplet was and still is an extremely good source of information and way to calculate just about any models CP. I regularly use this booklet when the currently available sim programs fail misurably in allowing the needed additions to a design to get a reasonable CP.
I'm not sure if these materials are available on-line anywhere, but if they can be found each of the 4 or 5 booklets are more then worth just about any price to download or purchase.
Below are a couple photos of the covers and a few pages from the CP calc phamplet. This is I think what the OP was really looking for in his original post.
Don't let the Math deter you! I'm no Math Wiz but use these calcualtions and Charts all the time. There is a real sense of accomplishment when you have your answer even though it may take a time or two to work it out. After a few runs you'll be able to complete these in just a few minutes. Shoot It take me longer to input a model in Roc-Sim then it does to use the old long hand calculations.
Hope this helps