I'm running Delo 400 15W-40 in my 261 and I have noticed a big change in how quiet the engine runs since I did it. I was using Valvoline 10W-40 and who knows what was used in the past. It still has the original cannister oil filter. I have also noticed less draft tube smoke. My engine is, as far as I know, original '62 and has never been rebuilt. It had the green paint still on it when I got it. It has bad valve guide seals so it smokes a little, but the Delo has really cleaned a lot of sludge out of the engine and the valvetrain is a lot quieter and smoother now.
