Differential gears, 67 c10

[RTHarvey]

I recently acquired a 1967 c10. There is quite a whine at highway speed, and I believe it is coming from the differential. My experience has been that this kind of noise is usually due to worn out ring/pinion gears. I am getting close to having it taken apart and examined. Assuming that I am correct and the ring and pinion gears need to be replaced, where is the best place to buy new gears? (hopefully without breading the bank) The SPID makes no mention of any rear axle option, which I think means it is standard, which I think is 3.73:1. This will generally be a gently and infrequently used truck. It is a 283, 4-speed, long-narrow. Any suggestions would be appreciated. Also if any of the assumptions I have made above (like gear ratio) are incorrect, I would appreciate being set straight.