What fuel delivery system did you have on your 4430? That was 53 yrs ago. From what I read, probably longer than the average reader age here on AT.

Could it be the high pressure, timed injection of today (2026) is by itself creating cleaner air? Does the direct injection of a modern 5.3 Silverado seem to burn cleaner than '62 Impala/409 w/a pair of dual Carters? 

Did you ever see personally, or see photos of the early B52 bombers taking off with black smoke coming from all 8 straight pipes? Watch a B52 now that they have the modern turbofans. No smoke. No Def either, and lots more h.p.

Maybe some of the clean air has nothing to do with Def or regen.