What 833 do you have? You probably could use a 3.09 first gear 4spd. they came in 64-66 sl/6 4spds, and I think some if not all overdrive 4spds. I would also suggest a 3.23 or maybe a 3.55 rear gear. That will help a lot in traffic and hills.
When I overhauled the transmission, I remember the casting numbers and gear teeth matching a 1964 - 4 spd, and the side - shifter plate being the latter model, reinforced plate with '64 era shifter forks.
At some point, I'd like to entertain different rear end gears. For now, I appreciate the 1st gear synchro when turning corners in town and will settle with shifting into 3rd when I approach a hill under 60 MPH. With my foot in it, 2nd to 3rd can be at 55 MPH.
:steering: