I just swapped in a 5.0 in my Jeep bolted to a Ford NP435 tranny. I used the M.O.R.E. motor mounts and an very pleased with them...excellent quality.
Couple of things to consider on the engine side:
The 88-92 Ford Mustang engines were MAF (mass air flow) HO (high output) engines. The 87 Mustang, and all the cougar/Crown Vic/Marquis/etc. are speed density and use a MAP (manifold absolute pressure) sensor INSTEAD of the MAF. When doing this swap you have to lay everything out about the engine BEFORE you start...trust me on this one. If you are going to grab an engine that is speed density, you better grab the entire harness and computer. I found out the hard way that all the aftermarket harnesses I could find were for the HO engines that are MAF. This includes Painless, and the Ford Motorsports harnesses. They will not work with a speed density setup. The computers are different also. I ended up converting mine to MAF. If you can get the whole harness from a MAP setup than go for it, just a warning. Also, the MAP setups are not HO and don't make quite as much power, but I'm not sure what you are trying to accomplish so that may not be an issue. If you want to convert it to a MAF HO setup you have to replace the computer and CAM and Heads and add a MAF sensor with housing, a BAP (barometric pressure sensor), HO intake manifold and exhaust manifold (will be a big bottleneck) and change the firing order to the 351 windsor order.
Also, the stock exhaust manifolds will most likely not clear the clutch linkage on the drivers side, and you will have to get really creative or get a set of aftermarket headers that will clear this area.
I would do a ton of research on what engine you have your eye on, because there are a bunch of little differences in the different years, computers, setups, etc. There are many flavors of 5.0 setups out there. I would also check out Corral dot net
as they have a plethera of knowledge on 5.0's and a classifieds section for all the little stuff you will forget, and need at the last minute. [img]images/graemlins/thud.gif[/img]