What's the diff in a '71 & later 727 TF from '70 & earlier??

[69RTSEV88]

I bought a B & M Shift kit for my 727 Torqueflite that is in my 69 Charger.  I kind of knew that the trans wasn't original, but I wasn't sure how to read the numbers at first.  The kit that I got says its for 66-70 727's, and that there is a different kit for later tranny's.  Well guess what, I did a little research and it turns out that the PK3681864 # stamped in the left side of the my case indicates its a '74-'75 tranny.  So my question is again, does anyone know what changed in '71 that would make B & M produce two different shift kits??
Thanks

[RD]

valve body, bellville spring, front servo design, front pump vent re-engineered different, transmission mount on tailshaft different... and other little things.

the main thing you are going to have to deal with is the valve bodies being different as the 71 and later VBs had additional fluid passages which will cause for different shift template plates than what you currently possess with the 66-70 shift kit you bought.  return it and get the 71 and up kit.

[John_Kunkel]

If the B&M kit is their Shift Improver do yourself a favor and feed it to your garbage can. Their Transpak is a much better kit and fits many years.

Better yet is the TransGo TF-2 and it's cheaper than the Transpak