I'm looking at different shifters including the B&M Pro-Stick. Are there plates or something in the mechanism that I can swap out to make it work with my 727 if I find a screamin' deal at the swap meet on a TH-350/400 version?

They are different. The 727 has a longer throw to get into park than a gm trans. Some shifters have changeable gates I don't know about the pro-stick. You will also need the correct brackets and shift lever at the trans the gm stuff if not compatible.

Not sure about the B&M prostick.

But I just installed a Hurst Pro-Matic2 in my Dart. Its the same shifter for Ford,GM,Chrysler. The shifter comes with different mounting brackets for the transmission end of the cable, and with transmission shift levers for ford,gm,chrysler. you just look at the instructions and figure out which one you need.

If your buying one at a swap meet, you could probably get the correct cable mount and trans lever from B&M.

I've only driven my Dart a couple times since installing the new shifter, but I love it so far.

Most shifters are universal, they supply different shift levers and brackets to match the throw of the shifter to that of the transmission.