[Captainfab]

The only direct bolt in rear differential swap for your '65 will be a '65- early '70 12 bolt from a C10. And those will all have the 6 lug wheel stud pattern. The most popular gear in these are 3.73's, which aren't a big step up from 4.10's but a little. You might get lucky and find a 3.08 geared rear differential, but I haven't seen very many. You would stand a better chance of finding a 3.08 or a 3.42 geared rear differential if you expand your search up thru '87. Of course there will be cutting and welding required for the installation of those. If you need a 6 lug, look at the K series trucks, or K5 Blazers. The 5 lug rears will of course be in the C series trucks. Also keep in mind that the '71-'87 rear differentials are 1.5" wider overall than your '65 rear differential. Another thing to consider is going to a taller tire.

BTW 4.10 gears aren't 'tall' gears, they are 'short' or low gears. A 3.08 would be a tall gear.