I'm doing the same conversion on my tired bird. It was a 383 727. I got the hump (125), found a guy with pedals/Zbar (300), paid 600 for a used 833. Paid another 800 to get it rebuilt locally, paid 300 for the bellhousing, another 300 for the clutch and flywheel (for a forged crank 440) another 550 for the Hurst Comp Plus shifter and install linkage kit.
Now I have almost 3 grand in a 4 speed that has no Overdrive. With a 3.23:1 - Posi Diff, 70 MPH is probably going to be around 2800 RPM. In Texas most freeway speeds are 75 - 80 to keep from getting run over. That is higher than I want to cruise at for more than a few miles. American Powertrain will sell a TKO500 or 600 with OD so you can cruise at 70- 80 at 2100-2200 RPM. The cost is about 3500 and everything is new. With the TKO OD is about .62:1, so you can run a 373 or even a 391 and still not be over 2300 RPM