since its a newer motor, shouldn't it already have a pickup tube? is it a good idea to use a screen or is it mandatory on the tube?
Yes, it will have a pickup tube, but its for the wrong oil pan. The Cherokee engine will have a rear sump pan which won't fit your Dart.
There's quite a few threads on swapping /6's to v8's, I just did it on my Duster. A quick list:
/6 to small block v8 conversion engine mounts (or new K member)
small block 904 transmission and shift linkage (or sb bell if manual)
exhaust system
v8 radiator (inlet/outlet are different)
Car oil pan and pickup (for truck v8 )
Wire harness will work, you may need to extend a few wires, no big deal. I didn't have to extend any of mine, but I did have to unwrap part of the harness and retape it to get the wires in the right spot.
This assumes the v8 is coming with all of its accessories. If its not, you'll need new pulleys, mounts and belts. The alternator and power steering pump can be reused, but you'll need v8 mounting brackets.
Your car also has /6 torsion bars, which will physically work, but realistically they were too small for the /6. A set of V8 bars at the least should be swapped in, although I'm a fan of 1" torsion bars on A bodies.
Brakes. If you've got 9" drums, you'll want to upgrade. If you increase your horsepower, you should increase your stopping power.
Rear axle. If you've got a 7 1/4" rear, you'll have to be really nice to it with a rebuilt v8 if you want it to last. And if you change the rear, you'll have to shorten the driveshaft.
Obviously, the torsion bars, brakes, and rear end aren't mandatory to get your car on the road. But, they're all things that should also be upgraded at some point, otherwise your new V8 car will handle and stop worse than your /6 car did, and will soon need a new rear end to replace the busted 7 1/4".
