Rear end for 1965 chevy pickup

[pooks64]

I have a 1965 chevy with 350 engine and a four speed trans in the floor. I have posi rear end but I think it's gear to 411.High rpms at 60 mph. I want around 307 or 340 (which is better)somewhere in that area. Should I have the gears change or should I look for another rear end? What year rear end whould have these gears? I'am looking for something for the long haul. I'am planning on keeping this truck for a long time.