3 different years, same transmission, which one should I use?

well you either ahve 904 tranny,s or small block 727 trannys.What you should do is this.The 66 273 is going to be a 904,the other two can be either a 904/727,the 76 car could be a 727.If it was me,I would use the 727.But go under and look at each tranny pan and see which one has the square pan and which has the odd shape corner one,that will be the 727 tranny.Mrmopartech
Now that my old site is back up and running,go to mymopar.com to the tool reference section and look at the tranny difference.