Rear end conversion question

[Kaptain Kadian]

Hello guys, I have just finished my serp swap and am looking for my next project for my 70 c10. I have a 383 stroker in it and a th350 transmission in it. When I get up around 65 or so, the motor seems like is is about to explode from the rpms. I don't have a tach, so I don't know exactly how many rpms I am at, but seems really high. I don't know what rear end gears I have in my truck, and I am pretty sure it is not the original axel for the truck. My question is what would be a good gear ratio to go with? I don't do any towing in the truck and mostly cruise around in it. The next quest is where is a good place to get said gears? Thanks guys.