I had a 1986 Chevy Astro van with a 4.3 V6. I used a metallic insulated "cloth" type heat shield which held in place by two stainless steel straps. This worked for me and I never had to change the starter. In the Astro van, the passenger side exhaust manifold IS A TUBE HEADER. It gets super hot in vans but the shield worked. If it didn't, I planned on putting in a metal shield also that went over the starter. As noted, I didn't need it. I can't promise this will work for you, but it did for me. I bought the "kit" from Summit but I don't know what the name was and this was twenty years ago.
Check out "YJ V6 Conversion" if you want to see a frame up restoration of my 1992 YJ.
Check out "WWII Jeep Photos AND Restoration of..." if you want to see the original JEEP in action...