New to restoring!!! Rear end help

[Sketchyfrog]

I recently purchased a 1970 C10 fleetside short bed. It's running a 327 with a performer cam and headers. 3 speed on the floor I believe the gears in the rear end are something like 4.65 gears. My tires are LT315-70R15. I have like a 50 mph top end you can see why I'm concerned lol. The gears are brand new. Is there a rear end that will bolt straight on with high 3's factory or am I pretty much going to have to cut? I want good torque but decent highway speed.