Depending on how much FORD ATF you put in, you most likely now have a mix of old Dextron and FORD...
TH350's shift quality is controlled by the modulator and the valve body pressure springs, plus the clearances in the clutch packs.
You are feeling a better shift quality most likely due to the FORD fluid having seal softeners built n, whereas DEXTRON, especially early blends, does not.
A 47 year old trans that's still running is an exception to the rule...good luck with it...but it will eventually require an overhaul....
