I've epoxied hundreds of things and what you're doing there will not have a high reliability attached. Epoxy is tough but 9 times out of 10 it will come loose from like a steel pan because of the different expansion rates between the plastic and the metal there, in short, the whole lump comes loose after a while. Not to mention you MUST get to the backside to guarantee it BONE DRY (last treatment in acetone or alcohol or forget doing it) for epoxy to stay stuck. Hot oil will leach under epoxy to gradually let it come loose, the temp changes encourage it. Already leached if the patch was not done on bone dry surface. Commonly on a patch like that I have drilled holes through pan and bolted or riveted down sheet metal patches to both sides with epoxy trapped underneath, that can last for many years. If crack is on a flat you can add an external metal patch over the glue to stretch out the length of time it lasts.
I use epoxy a lot but the common uses most use it for are mostly miserable failures, I watched it 9 times out of 10 at the parts store all day long. You have to put some thought to it rather than just slather it on there and hope for the best. Some applications simply will not work and based on conditions there. Most fail simply by not being clean enough.
You absolutely cannot braze the pan with it on car, do so and find out one of several reasons why. BTDT. For one you'll catch the remaining oil (even if drained) in motor on fire.
Maybe if the Pinto is one with mechanical rod linkage and not cable? Having to lift engine to remove pan might damage the linkage.