This thread is going to describe in detail exactly how I put the LS2 drivetrain into my '91 mustang. I know there are several different ways to accomplish the same results and I'll try to touch on what I know, but I'm mainly going to stick to what I have personally done with my car in my garage. Save the drama for you moma and go talk about cleveland heads, building motors on your tailgate, and tuning with only a flathead screwdriver for another day. This is strictly for information about the LSx swap process and not if it's a good idea or not. Now that that's out of the way, onto the tech....
Once you have obtained your choice of LSx engine and fox car you probably want to know how to mount the GM engine into the Ford chassis. Surprisingly the LSx fits into the fox platform very well. It is an extremely compact engine and this is much less work than it seems. Regardless of the LSx engine you decide to use, you will more than likely want to get and F-body oil pan because it fits the best in the fox chassis IMO. Some guys have used the truck pans, but they do hang down lower and you really gain nothing in return unless it is free or you just have it lying around. I used the F-body pan. I also used my existing MM K-member and built my first set of engine mounts from used ford 4.6 mod motor mounts and some 67-72 Duster/Demon/Dart mounts. They worked fine, but I ended up building another set out of F-body poly "clamshell" poly mounts and making adapters that fit these mounts to the K-member.
AJE now makes a k-member for mustangs with LSx mounts already on it and it looks like a pretty decent piece. I would not use one on my car because I have larger brakes/front tires and drive it on the street a lot. I'm sure it would be fine for a drag/grudge car or a cruiser. Here is the first set of mounts I built. I might have a few pictures of the new set I built, but I'll have to dig them up later. I built my mounts to place the engine as low and far back in the engine bay as possible for obvious reasons.
4.6 driver side
in the car
passenger side in the car
Engine in the car. 6.0L of displacement and it sits lower than the stock 5.0 does......
Coil to brake booster clearance. I was worried about this one because I'm running a big SN95 booster for my brakes and thought it would be very close. I was right, but it fits...
I'll post up the next part with the transmission mount later.