May or may not be helpful info:

One time I was resetting the timing on my engine after I removed and replaced the distributor, and the first time I started it up was interesting. The engine was bucking and shaking and there were high pitched hissing sounds to the point I thought I had forgotten to tighten/install something and seriously damaged my engine by starting it. I was seriously concerned I had destroyed something by the noises it was making. Sounded like as if I had changed the oil with 2 lbs of beach sand.

I adjusted the distributor by "feel" then timed it up with the light and had no problems. So my vote would be time first, then be concerned if it doesn't fix the problem.

I'd also hypothesize that a "way out of timing" 4 cyl would idle rougher than the same timing on a 6, since there are less rotational mass to even out the ignition.
^^^^^^^^^^^^only a SWAG though, could be incorrect.