All of my 1970 and up outboard carbs, 4 sets, have .078 holes, centers about .002 bigger. I do not have any 69 carbs. I am up to .081 on mine and need more as the dist port has vacuum at idle. It will idle at 750 with no vacuum, but I want it at about 950, so about 10-20% more drill area, probably about .085-.090, need to do some r2 x pie math. It would not suprise me if replacement plates are blank. I think .075 would be a safe start.