if you have a timing light, as Jeff said look at the light and see which cylinder drops, then you can swap 2 coils positive wires and plug loads, if the problem moves your coils are fine.
since we are all cheapskate, build yourself a diy dva adapter for $5 and test the trigger and stator. I had a 60hp 1985 same issue, just checking ohms on the 3 trigger wires showed a difference, after testing dva I found a drop right before the miss.
swapped trigger and worked fine since. I recorded some videos yesterday testing these mercs check YouTube in about a week or I'll try post a link here..