65 904 vs 66-up 904 differences/advantages?

I forgot exactly what year it changed (mid 60's), but the newer 904 transmissions have different converter splines and a larger snout. That means that converters won't interchange and a newer converter snout won't fit into the crank register. You may need a newer style custom converter but with the older style, smaller snout to fit into the crank. In 1978, Torqueflites started using lock-up converters, which were also splined differently and won't interchange with non-lock-up versions. But they retained the bigger snout. They are fine for stock street use, but not performance oriented. Best thing is that they also started getting lower first & second gears about then or shortly afterwards. I believe speedometer cables and gears were changed around then as well.