If it were me:
Personally I like a tight rear, 4:11 or 3:90's.
First, I would want to know what is the ideal power curve for this motor, ideal, max hp, and torque, RPM's, etc. Chevy can give you that. I would work everything toward it.
Second, What size tires am I running? How about a taller tire and 16 inch rims for the six lugs are everywhere. I personally would shoot for 31" tall.
Third, I would go for a different tranny. One with an OD. Can take advantage of the 4:11 on take off and cruising on highway OD would run less than 1:1, maybe .72'ish. This should put my 70 MPH RPM at 2200 or there abouts.
If I have to downshift to pass a car I would consider more and progressive carboration.
Cavebull
Crap..! I'm confused.. The bigger tire idea was first suggested to me by my rear end guy.. I have the 15 inch rims on there now. I'm sure they came with the truck.. Actually, this truck was pretty un-bastardized when I received it.. I wanted to get some bigger rims that looked more stock but I couldn't find any.. Partially because I really didn't know what I was looking for or what to call them.. This is all new to me..
I looked in various catalogs that have Chevy parts and they all only gave 4 options for the ring and pinion replacements on my particular model engine and transmission.. The 3:90 wasn't one of them.. 4:10, 3:72, 3:55 and a really low one around 4:50ish..
Also, If I upped the rim and tire size to 16 inch rims and a 31 inch tire, I would have to re-calibrate my speed and odometer.. Which I'm fine with..
So I guess the three questions I have for this avenue would be: Would sizing up the rim and tires and re-calibrating the speed/odometer save me gas mileage? And would it be cheaper than having the ring and pinion changed out? And finally, could I still get those old school half moon hub caps on a 16 inch rim? I assume Chevy sold 16 inch rims as an option in those days?
The transmission change and or the overdrive options seem like they would be a big expense and a bit more than I would want to put into this vehicle at this point..
And finally, as far as obtaining the specs from Chevy, if you had a link I could hit up for that I would love it..
Thanks again.. I'm not a real mechanic and I really only know a little.. So I appreciate help and input from this forum.. Hell..!! My rear end guy told me to go on here and he's suppose to be an expert..
