Tranny swap

[macleay]

Hi. Newbie owner here. I have a 65 c20 with a 283 High Torque engine and Saginaw 3 speed with 4.71 rearend gears I believe.
My question is: What tranny can I bolt in to give me a higher top end? Right now I'm not comfortable doing much over 50-55 mph. I'd like to be able to cruise around 70 without damaging the engine.
And is there a cheap tilt column replacement? Like another model chevy that can be pulled from a wrecking yard and dropped in? My big ol' belly would appreciate it! lol