I think that you should call MM. They can give you all the details you want/need and hook you up with a great handling suspension. Depending on what you actually intend to do with the car will determine where you should go and how aggressive to go. First you must decide if you want a street terror for carving up your local back roads, an autox machine, open track wonder, drift machine, or a mix of all.
Plates and SFC's would be a great start. If you can find someone in your area to properly install the subframe connectors then go for it. If not, you might want to pass on that for now. The CC plates will be a good way to adjust your camber and caster which will aid in handling. A PHB woudl be a nice addition as well because it will give you good lateral control, once you move into any heavily competitive or aggressive driving you will want to come up with some kind of solution to replace the upper control arms as they are a big problem in the stock setup. Enter the TA setup, 3 link, or even Steeda 5-Link.
Coil overs would probably do wonders for you front suspension and handling. If you are going to install those up front, a GOOD set of CC plates is mandatory. While you are in there, a strut bar may add additional rigidity that could be beneficial in a coil over application.
Thant should be plenty to get started.
Your 91 240 may walk "all over" your Cobra, but it sounds like it has had a healthy dose of mods as well seeing as it did not come with a turbo motor. Give the Mustang platform a chance, it will take some manipulating, but I think it can be pretty good and most people here tend to agree.
So there is my $.02 which is just a basic summary of what is already available through search. If you think it is bad here then you should try corner-carvers.com.