WHAT VEHICLE IS THIS GOING INTO?
I would connect a scan tool to the donor vehicle, run the engine, and verify that all the sensors, and all the outputs--injectors, EGR, spark timing, etc. worked properly BEFORE you yank the engine. Maybe even do a cranking compression and/or cylinder leakdown test. Verify hot, idle oil pressure.
V-8 is heavier than V-6. MAYBE you won't notice much difference in ride height, but it'll likely be enough to throw off your headlight aim. IF this is going into a 4WD, you'd just turn the torsion bar adjustment if needed. A 2WD MIGHT require the front springs from the donor. Which then gets you into rebuilding the front suspension of your truck. Which then gets you into upgrading the brakes, assuming that the donor truck has better brakes than your truck. Donor probably has JB5 brakes, a big upgrade in the front from JB3. Look at your glovebox decal to see what you have now.
I'd look real hard at your existing radiator. You may want a larger one, or one that isn't corroded/clogged. Inspect the fan clutch and fan, too. Might be that the V-8 uses a larger fan, or one with more blades/steeper pitch. V-8 probably uses different radiator hoses, too. Flush the coolant!
The quick-coupler for the heater supply hose on the intake is notorious for corrosion failure. Believe it or not, the Dorman replacement is actually BETTER than the OEM unit. I have a Dorman unit I installed over twenty years ago, and it outlasted that engine. I transferred it to the new engine, it was still in "perfect" condition.
I don't install an engine without shoving in a block heater. If you live in an area with cold weather, now is the time to put it in. When the core plug comes out to install the heater--look at the back side for signs of rust. If it's rusty, REPLACE ALL THE OTHER CORE PLUGS. I'd also remove the block drain on the driver's side, drain all the coolant, and replace it with either a brass plug, or a brass draincock. The right side block drain is used for the knock sensor, which you need to retain from the V-8 engine. I'd pull it out, drain the coolant on that side, make sure there's no buildup of rust in the water jacket, then reinstall to the proper torque.
Of course, you need the TBI unit with injectors to suit the new engine. The base gasket for the TBI seems to be a higher-failure item, you'd likely want to replace it.
Verify that the rear main seal doesn't leak. Assure that the torsional damper doesn't have failing rubber, and that TDC on the damper/timing pointer aligns with actual TDC on #1. Decide if you want to "Reseal" the engine--replace all seals and gaskets, perhaps including valve stem seals.
Does the donor truck use the same transmission as yours? A V-8 trans is probably build with different calibration and/or more clutch plates in the drums than a V-6 trans.
While it would be nice to install fresh engine mounts, I haven't found suitable ones for a 4WD. The 2WD mounts may still be available from a quality supplier--not the Made In China garbage that the 4WD versions get. I looked at several options when I installed the newest engine, and ended-up putting my original 300,000-mile mounts right back in because everything else was JUNK or didn't fit properly.
I'm told that the V-6 air intake from the passenger fender does not have a silencer built-in. This is an advantage from an air-flow perspective. The V-8 silencer is--apparently--restrictive. Might want to keep your V-6 air intake system.
This is the time to be thinking of installing headers, a low-restriction catalyst, high-flow Y-pipe, better muffler and pipes, etc.
Obviously, fresh oil and filter, fresh coolant, good time to flush the PS fluid, flush the trans fluid and replace the filter. Verify fuel pressure, replace fuel filter, inspect air filter and hot-air diverter flap in the air cleaner. Verify cap, rotor, plug wires, plugs are in good condition. LOOK AT THE DISTRIBUTOR GEAR AND MAINSHAFT, assure that the magnet on the main shaft for the pickup coil isn't broken--VERY COMMON! Route the plug wires exactly the way it shows in the service manual, including all the brittle plastic retainers--doubly-true for #5 and 7.
I'd rather use a stock torque converter than a cheap mass-market "Performance" converter from the "big names" like B&M, TCI, etc. If you want a "Performance" torque converter, you're going to need to spend real money for one. But now is the time...
