6.0 in 58

[yossarian19]

I typed out a pretty good ramble but here's the short version of what I learned putting a 4.8 / 4L60E in my 1957...

You want to stuff it as far toward the firewall as you can, or you won't have space for an electric fan on the "pull" side. It's a PITA to try and get a fan onto the "push" side of the radiator.
You still need space to hook up the oil pressure sender & access the back of the motor, though.
The crank pulley has to be kept clear of the front cross member, which is a compromise between fore-aft placement and up-down placement.
You've got the 4L80e behind the 6.0, I assume, which means going too high isn't an option - so again, it will be slammed up on the firewall.
The factory rear crossmember has to go. You can get the trans in there with the thing in place but you can't get it out again without pulling the motor. IIRC, the tailshaft angle is all wrong too. Sheet metal / frame clearance.
I'd box the frame while you're doing this. Why not?
Unless you're very, very good with a tape measure - I'd get the Dirty Dingo sliding motor mounts & some weld-in SBC engine mounts. The Dingos will let you fudge a little bit.
Factory exhaust manifolds fit but only just barely. Well under 1/2" clearance to either side of the frame.
Power steering becomes a must because the factory box won't clear the manifolds.
There are no off-the-shelf solutions for the radiator. I had mine modified at a radiator shop. Not sure that was the best solution but it seems to be working so far.
Fuel system - many, many options. The Mustang tank is not as trouble-free as it seems. You have to modify the rear frame rails, which means removing the bed. I didn't remove the bed and did a lot of it half-blind, which made a mess of things...Looking back, I wish I'd stayed with the tank in the cab or gone with a custom tank & walbro pump. Keeping the filler in place, just keep the factory tank. Use a fitting on the bottom of the tank and let a Walbro 255 LPH pump suck fuel from there. You may want some kind of sump in the tank, so look into your options there. The Walbro can push fuel into a 2003 Corvette fuel filter / regulator & return fuel to the tank, if you have a returnless rail engine. If you have an older 6.0 with return style fuel rails, you can use a Camaro LS1 or Tahoe / Silverado style filter. Whatever's easy to plumb.
I used Dorman nylon fuel line. It's easy to work with, OEM approved and a hell of a lot cheaper than AN stuff, which is just bling for most of us.
What else...
Custom driveshafts, of course.
Steering linkage to oil pan shouldn't be an issue for you, since you are going 4wd. On a stock front axle.. it's an issue with the truck pan.
Aaannd... making the engine stand-alone isn't real hard. Making the wiring look clean, I thought was hard. I recommend doing all the wiring with the engine out of the car & on a stand, or on a pallet, with the transmission attached. You don't want to be walking back and forth with a tape measure trying to guesstimate three dimensions of wiring & cutting things to the right length +- 6". Trust me.
Other than all that... easy-peesy.