decodeing 273 from 1964 plymouth
For it to be a 1964 833 it will have a ball and trunion output shaft flange instead of a slip yoke. If the tailshaft does not have a bolt on driveshaft flange it is not a 1964/65 trans, unless someone has swapped out parts from a newer unit.
To tell a four speed from a 3 speed
3 speed has 2 shift rod mounts in a row
4 speed has 2 shift rod mounts in a row and a 3rd shift rod mount down low
The included link is an example of a 1965/66 and later four speed. I am not real sure on what year each engine stopped using the ball and trunion, but all 1964 models had them.
http://compare.ebay.com/like/190490367229?var=lv<yp=AllFixedPriceItemTypes&var=sbar
And here is some reading on the variation of the 833
http://www.slantsix.org/articles/4-speeds/ODA833fourspeed1.htm