Regarding the speedometer gear mentioned by doyle1950, many years ago when I changed the differential gears in my 1958 1/2 ton panel truck (went from 4.11-1 to 3.80-1), I went to a local speedometer shop for help.
They calculated the gearing that I needed vs. what was in the truck from the previous gears (stock) and built me a little adapter that on one side screwed into the side of the transmission and on the other side accepted the speedometer cable.
That little adapter (a tiny gearbox in itself) made the speedometer read correctly. I was a very happy camper!
Cheers, Dean
