68 5000 gasser questions

Been working on my "new" 5000 gasser all summer. Had serious problems with backfiring, afterfiring, coughing, sputtering etc both when idling running throttle up and down as well as when it went under load. Tested compression and to my surprise, all cylinders were between 130 - 135 ! I decided to invest it getting it back to running reliably. Problems turned out to be mainly distributor timing, both mechanical and vacuum advance didn't work at all, so total rebuild on dizzy. Also had some Holley carb issues thrown in for good measure, so I upgraded to a new Zenith. Put electronic ignition in, alternator conversion changed wires, plugs, cap etc.
So I got her running well right now but have 2 remaining items that I would like to try and see if I can fix or should just leave it and live with it.
1) When I run throttle up quickly it will backfire out the carb once or twice until it catches up. If I run the throttle up smoothly, no problem. Throttle down is not a problem. So question is, is this sorta normal ? If not any suggestions on how to improve on it ? Or should I just leave it and live with it ?
2) Plugs look normal, except for cylinder 2 and 3. When I pull the plugs to check them after running tractor up to temp #2 and #3 show oil on the threads and a little on the plug itself. Is this a major issue ? Or should I leave it and live with it ?
Thanks
Alan

No accelerator valve/pump contributes to the momentary lean response when you goose it?..Remember that goosing it under no load is different than when the governor feeds it under load. and maybe some valve guide wear on the valve stems leaking oil into the chamber? So if it plows good, drive more and worry less. Good job.

What is "plug itself"? inside or outside?

When I pull the plug out I notice oil on the threads and it looks like a drip of oil on the bottom of the ground electrode, not the central electrode but the one that is attached to the threads. Almost like when I pulled the plug I hit the electrode on something that had oil on it. If memory serves me I think I saw the white insulator around the central electrode look wet as well.