Rear Differential Rebuild Questions

So I am looking into having my differential rebuilt. I have read all the threads about rebuilds, ring gears and wheel bearing replacements. From what I have gathered, the problem with mine is the ring gear is badly worn and starts howling around 40mph and quiets down around 60mph(which is also the top speed). I would like to be able to take road trips and cruise around 70mph while getting better MPG. My wife and I have a small furniture business on the side and use the van for pick-ups and deliveries. It would be nice to extend our range farther than the greater St. Louis area.

Here is where things are different than most of the rebuild threads I have read on this site. I want to keep the 3-speed manual while changing my rear end ratio to 3:08, or something that will get me at a comfortable highway speed with stability in traffic. It seems a lot of you are opting for the upgraded overdrive or auto transmission plus the upgraded differential ratio. I find the stock tranny fun to drive (still got young knees).

So without changing out the transmission, what are my options. I haven't opened the differential to find out my current ratio, but from what I feel when driving and have read, it is most likely a 3:36. Questions listed below:

- If I change to a 3:08 rear with stock tranny, will I be able to comfortably be able to cruise around 70mph?

- If I am in traffic and it comes to a slow roll, will 2nd gear have enough power to pick it back up without stalling since first gear has no syncros?

- Any other setup that would work best with the stock tranny to reach my goals?

Let me know what you guys think. Either way I have to get the ring gear changed out, but I would like to get some upgrades while everything is open.

- Charlie
65 Chevy - Straight Six 230 engine - 3-speed

You've probably seen one of these but they are fun to toy with while figuring this kind of stuff out. http://www.corral.net/tech/gearcalc.html
It's my personal opinon that 70 mph in an early and the word comfortable don't go together.. but yeah ya can do it ! LOL maybe some of the 6 banger guys can chime in here and say what RPM the 230 still has some OOOMFF at. Dropping to a 3.08 only gains a couple hundred RPM by the chart but that may be an important couple hundred ?

a 350 411 will do the same but a 327 gets better miles w. same power but the chevy 6 has seven main bearings

Thanks for the replies. 65mph is also better than 60mph. I don't have tachometer, so finding out the RPM's will be hard.

I am going to have to have them open it up anyway, so when I get the exact ratio I will be able to figure out more. Was there a stock 10 bolt differential that had 4:11 ratio in it? Mine has quite a bit of torque but no high end cruising, just pushing the engine hard on the highway.