There are so many ways to skin this cat, I can't possibly talk about every option but i could tell you what I did and why I did it that way.
I used KDS mounts, they keep the engine in the same location, same crank centerline and same distance back from factory to maintain factory drivetrain geometry. Many guys use adj mounts but they usually lift the motor up and forward and I really don't like the idea of moving the single heaviest part of an 18 foot long car further forward, even if only a slight bit. The KDS mounts make some things easier, like oil pan and header choices but leave you less room to the K member for different accessory drives since the motor is further back.
For the crossmember. I went with Clear Image Automotive. Dan has never failed me, always builds great products. The 80e took a slight bit of denting to one floor pan and a tiny bit near the trans cooler fittings (i'm using AN) but nothing a few hammer blows couldn't fix.
Oil pan, the KDS mounts are designed to work with either an F body oil pan or Holley. I used an F body pan with an Improved Racing internal baffle kit since if you're swapping in an LS engine to do LS stuff with, you'll probably want improved oil control (unless you're only planning to make like 400hp in which case why even go LS).
KDS mounts are also designed to work with F body headers, but they require trimming of the A arm support straps. I notched mine and welded a support to the back side but most guys just cut them out. I tried TSP 1 7/8 3" collector headers and the d side hung too low for my liking. I ended up going to 3 Pedal's B body swap headers. They are beautiful and fit great, give you plenty of clearance everywhere and don't burn up ignition wires or anything. They appear like they would have fit without cutting the A arm support strap as well. I hear Speed Engineering F body headers also fit very well and for a fraction of the price the 3 pedals headers.
AC, I forgot most of the stuff I learned when experimenting with various AC setups but you should be able to run a truck drive and a mini compressor like a sanden SD7b10 without chassis modification using KDS mounts but don't quote me on that. I notched my K member it and was able to get a full-size to fit on truck spacing but decided not to go that route and went with a high mount setup instead from LSX concepts. They make beautiful kits, especially if you plan on using an LSA blower like me, but also very nice stuff for non SC'd setups. Pricey but it was worth every penny for me to keep my independent blower drive, use a tensioner setup that doesn't miss a beat at 16PSI and maintain a full-size AC compressor similar in volume to the factory compressor to keep the AC functioning effectively.
For the wiring, really can't help you there as it depends on how you plan on doing it, what you plan on using and i'm not familiar with what systems are on an 04 that may not be re-used for the swap. There will obviously be a lot to remove from your factory harness i.e; all of the engine control wiring. Fan relays some keep the factory fan harness and relays from the factory fuse box and just use the ECU's relay trigger from the new harness, which allows you to delete the fan wiring. Fuel pump depends on whether or not you are running something big/aftermarket or not. For me, I ran completely separate fuel pump wiring for my twin pump setups and just used the trigger from the new ECU to activate the relays so the rest of the fuel pump wiring could go.
