I actually have a GIGANTIC roll of the stuff shown below. It is adhesive backed and it’s what I used to reflect heat from the underside of my hood. I figure if I cut it into strips I can wrap the section of the wiring harness that goes across the block. That way it will be wrapped in wire loom, electrical tape and then this stuff. It should be fine to just rest on top of the engine block then.
That way the regular wrapped plastic wire loom will be fine in the areas that it was just laying on the heads before, and the section that was connected to the OEM manifold suspended above the engine before will be wrapped in this crazy 500F direct, 1100F radiant, resistant fiberglass wrap.
Since it is all silver it should better blend in with the engine block