What spark plugs?

looks like a tad too much total timing by the way the tang looks.

maybe try 32* total, initial don't look bad, not to say you couldn't run a lil more.

yellowing on the tang from heat/or some kind of fuel deposit.

if you look down into the plug, what color is it where the ceramic meets the steel body?
you may be a lil rich in the primary.
you could go 2 steps lower in the primary and see if it surges at 50 mph cruise, if not go another jet down till it just starts to surge, then go back up 2 jets.