Overdrive options query

Hi:
I am mid-project on my '52 F1. It has a Saginaw (456) four-speed in it and the original rear-end (3.92). Trans is prior owner install, so I am using it. I am thinking for down the road the options to make it more enjoyable on the road. That brings me to overdrive units for better highway speeds. I know generalities for add-on overdrive units but no specifics. My only experience with overdrive was my first car: a '59 T-Bird with a 3-on-the-tree and an electric overdrive (yes, a rare Bird). The overdrive was integral to the trans and the servo was part of the tail shaft. To me, it was part of the original design, not an add-on.
Who, or where, are good sources to find out more info on what is available and what is recommended? Are there overdrive units that "replace" the tail shaft on specific trans? Or, are there an add-on part after the output shaft? I'm not looking for the overly expensive custom, chromed, digital new stuff. Something that works, reliably, and not too "custom" to install. Does it exist?
Thanks in advance.
William

How original is your F-1, and has surgery already been done on the transmission support cross member?

Ford actually set pickups up with OD units in the F100 years. The best unit is the T85 with the R11 overdrive. Ford used them till 1970 or so in pickups. The R10 behind the Ford 259 series transmission is a lighter duty unit but still viable for flathead use. There are still units out there including the 1949 through early 51 Mercury that will bolt right up to a Ford half bell on a pickup. The will work with a pickup clutch set up.