Look at it this way---a 1986 freewheel is 20 year old technology, even if it's just the ramping or the tool used to cut the cog teeth. If you're using the same shifters, 6-sp indexed, I assume, you're fine and probably better off with an IRD or a newer Shimano, even the cheaper ones.
I use a GT chain right now, but find the inexpensive SRAM's to work just fine. A good Shimano chain has been smoother on a couple of my freewheel bikes, but $40 vs. $15.