Difference in 5.0 heads

Someone more familiar with the markings etc.. can answer what I don't but I'll make what you're considering an easy decision for you. 86 GT heads suck and they're good for nothing more than holding doors open or papers down and I wouldn't swap them onto anything. As for swapping the other way. It's very inlikely that you'll get away with it because the 86 GT 5'oh has flat top pistons and compression that's right around 9.2. What that means that most heads (including facotry heads) from other years etc cause a piston to valve clearance problem. Ina nut shell... either way the swap is not very feasable unless you plan to fly cut the pistons on the 86 block.