Check with member
TOW4. He sells rebuild kits, and I think he may have what you need to not only rebuild it, but convert a standard one to isolated ground.
If you don't want to go that route, search for "isolated ground Delco 27". I just did that and turned up an
Amazon listing. I have no clue if the seller is reputable, but it shows they are out there.
By the way, You don't have an 86. You have an 84. The Army didn't want the hassle of dealing with model year changes in their supply chain, so they required them all to be built to 84 specs. When you need parts, you want 1984 parts, no matter if your truck was built in 84, 85, or 86.