Steve, FWIW your Goose upper cast aluminum mounts and the rubber bushings with bonded steel washers you show, look identical to a Pantera upper mount. Pantera 351-Cs run at least as hot as a 289/302 in a Mangusta, so don't worry too much about the heat-reliablity of the rubber insulators. Just don't use polyurethane, which will melt!
What I would worry about is frying the lube out of that front heim joint next to your heat shield. Also FWIW, the Pantera uses a 3-layer sandwich of aluminum, asbestos (or maybe fiberglas, now) and aluminum on our gas tank heat shields, and this stuff is available from the vendors. It bends like dead-soft alum sheet so its easy to shape.
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