RE: 87 350 missing and running rough
Since he's got new plugs in it, check them to see if they are fouled, sometimes too much fuel you'll be able to tell by looking at the spark plugs.
You say it gets sluggish once it's up to operating temp. During warm-up, thefuel system doesn't use the 02 sensor, but once it's at operating temp, it does, have you checked it or are you not getting an engine code?
I don't know what your motor calls for, but I would thinkthe timingwould need to be at around 8 degrees advance. But that might not matter...