I have a 52 panel with a 350/350,and the stock rear end from a mid-70's 1/2 ton. I wish I had either an auto trans with overdrive or had used a good 5 speed with a big overdrive gear, like a New Venture 4500. Don't put in a 350 hydro-- the gas mileage and engine revs are not pleasant.
Now I am building a 56 3/4 ton, and that is what I am doing-- computer controlled small block and a NV 4500. But don't dream that you are going to come out of this for less than $700. It will cost several times that, even if you use mostly new parts.
My "new" 56 has no motor, so I have to do something. When I changed over my 52, the new tall rearend gears were not available. If I were to do it now, though, I would keep the original engine and change the gearing. It is just a cleaner job, and just as nice to drive. I have power discs now, and they are not enough better than the stock brakes to merit the money and effort it took to make that switch, either.
Vttinkerer