An update to the above info:
For the hose that runs from the thermostat housing to the firewall, I now prefer this solution achieve the reduction and improved routing that limits risk of fuel damage to hoses:
Instead of seeking out a 5/8"x7/8" metal reducer, just order TWO of those abovementioned cheapo Rabbit hoses (PN above). Use the first at the rear of the head, and use the second in this position on the side of the engine. It connects to the tee (where the cold start thermostat return enters) and then provides the needed size reduction plus kicks the hose routing out towards the strut tower and away from the fuel pump. Then just use a direct 5/8" coupling barb to continue this hose to the firewall with a section of standard bulk heater hose.
Tip on that coupling (and also for the one at the back of the head connecting the Rabbit hose to bulk hose there): a brass 3/4" PEX union makes a perfect size, low cost, strong coupler for 5/8" automotive hose, readily found in the plumbing aisle at your friendly local hardware store.
I need to add pictures to this thread; will do that next time I get the chance.