RE: Wanna make mold of this cowl, how?
I see now. The cowl flaps have clearances for the exhaust outlets. The scoop on top and bottom is an addition. Your plug will require 'dams' around the cutouts. Kinda like a parting board but there is no way it can be flat unless you fill in the cutouts to be cut back later as cowls fabbed from molds to be installed on nacelles. The firewall nose bowl will have to be separate item.
Can you separate the firewall nose bowl from the rest? Can you add foam to the rear portion once you separate the two? If you can add to the rear portion the parting board is a piece of cake. If this can't be done then send to me a full sized paper 3-view and I'll spin a new cowl plug for you. I'll have it painted and everything by around February. I don't put panel lines or rivet details on them because they look cartoonish molded into the part. That detail, to me, is best left at the 'final primer just before painting' stage. I can't do this right now because I'm building a pedal plane as a Christmas present. However, you never know!