Hallo,
It is a good idea SE, but I would use rather the wooden pattern which can be made of medium hard balsa, for instance.A balsa strip circular in cross-section is a good thing for this.The dimensions of the con you can take from the P-51 drawings.You must remember you should minus the thickness of the plastic sheet from total dimensions of the con. When the strip is "sharpened" at the top, you can warm up a small sheet (plate) of plastic and stretch on this pattern.Cut off the part you need and you have.
But it's up to you only which of these ways you will choose.
regards,