Like others have said wrap the headers with the old school style heat wrap. The cheap cloth type usally works good. Go around twice to make sure they are good and stay in place.
Also use a piece of aluminum sheet in betwwen the headers and the starter helps if you have atleast a 1/2 inch air gap on each side. Im sure thats not going to work but try the best you can. The sheet can be pretty thin. It just needs to reflect heat. Dont paint it a little shiny metal will work better.
The factory used to use thin steel pipe to get the wires past the manifolds. A little piece of alum or steel pipe will allow you to run the wires past the headers. But you got to make sure its not going to rub and cut the wires. Gm usally flared both ends of the pipe so it never touched and edge. Also buy oem style heavy wire the kinds thats hard to bend the insulation has a higher temp. You cna buy wire with insulation good for 600 degrees just got to source the right stuff.
Now to the real problem why it is so freakin hot. I know the headers get hot but those old wagons usally had a lot of room. Is it running a little lean?