Upgrading '69 C10 to haul a car

[Spedy7]

So I'm a bit lost on this, I've been searching everywhere but can't find a solid answer. I want to upgrade my C10 to haul my '66 Mustang via open trailer (u-haul trailer) - what all should I be looking at? As its set up now, it was originally a 6 cylinder truck, but someone swapped in a 350/TH350. There's a small trans cooler, coil springs at the rear, bumper hitch (need a frame mount hitch for sure). Currently have no idea on rear end gears - my guess being somewhere around 3.50 or higher and I think a 12 bolt rear. Has drums all around and power brakes.

In total I'm guessing around 5000lbs for car+trailer (on the safe side - might also be throwing in some other stuff) - as it sits, would 3/4 ton springs swap right in? What all would you recommend I change out/upgrade?