Another thing to consider, althought it is hailed as the suspension used on nextel cup cars etc. They don't use it because they want to they use it because they don't have a choice its in the rules. It is a good suspension design and most definitely beyond what leaf springs are capable of. Keep in mind however, if nascar gave the cup drivers a choice they would almost undoubtedly be running a 3-link. Just something to think about.

I think a better way of deciding what type of suspension you are going to put under your car is to, first, decide what type of driving that you will be doing, primarily, with the car. If it is primarily street than you may want to look at enhancing the OEM suspension first. There's still a lot of suspension in there! If your going to be tracking the car or going to the drag strip more than 20% of the time then I would say 3 or 4 link. This is not to say that you can't run 3 or 4 link on the street but why spend the extra bucks if your not going to use it? If you are going to track it more than once in a while you may want to drive it as it is set up now and see what you don't like about the car and work on that.
My friend has a Truckarm from HTH in his 32 coupe and he loves it! He likes the fact that it has a lot of adjustability and he can tailor it to his specific needs. A couple of my other friends also have them and they also love them so it seems that for mostly street driving it seems to work pretty well but then again they aren't torqueing it as hard as they do in Nascar! As far as Nascar, keep in mind that there are many more variables that make those cars handle other than the truckarm itself!