Well, we have something else in common besides having worked on Mustangs and airplanes. I learned how to make gaskets with a ball peen hammer when I was a kid working on lawn mower engines for go-carts. That was over 55 years ago...
I've made a few upper intake gaskets in the past. I used gasket paper and this spray on red goo. The spray on goo sprays like spray paint and stays tacky. I spray it on the intake manifold and then press the gasket paper onto the intake with my hands. When I lift it off, the goo transfers to the paper and I have perfect lines to cut with a razor blade. I believe I got both the paper and the goo at the parts store. Has worked great when I've needed a gasket in a pinch. Never had an issue with leaks.
I never had any luck with the big bead of silicone. It seals initially, but within 20,000 miles it starts to leak again. I always use the rubber seals.