For the top to melt, it has to be running too hot. This is sometimes caused by a vacuum leak, but that would normally affect all the cylinders. My guess is that you have a partially clogged injector, not putting enough fuel out and causing that cylinder to run lean.
Good luck on honing the cylinder and just replacing one piston. Your odds are probably better than 50/50. My recommendation is to not use chrome rings on that cylinder. You might have problems getting them to seat. Don't just slap in the rings, make sure and check the end gap and adjust it if necessary.
Once you look at it and hone it, measure the cylinder size and see if it is still within spec or at least real close. Back in the day, you could get a piston that was a couple of thousandth oversize just for this situation. Don't know if they are still available. Just try and match what you have. If you get a different piston with a different dish, you will fight getting the engine to run smooth, and you will always have a slight vibe.
Since you have to pull the pan and rod anyway, check all the bearings. If they look good, then don't worry. If they are starting to wear, you might want to look at slapping in a fresh set of rod and main bearings. We used to use a leather belt and some cerium oxide to polish the crank a touch before swapping bearings. What ever you do, look at the bearings for markings, they may have been replaced before and if so you will need to match the size. The same goes for the pistons.
Again for preventative maintenance sake, since you have the head off, I would replace the valve seals and maybe lap the valves.
