Ok, take this for what you will but I've been researching suspension parts for mustangs since about 97.
The watts link is a "superior" method of centering the real axle when compared to the pan hard bar, as the watts will keep the axle centered and the BHP moves the axle from side to side with suspension travel. But the effect is minimal and actually counteracts the effect of engine torque on the rearend (drive shaft torques the rearend right and the PHB torques it left (or visa versa, can't remeber which). So all in all, I wouldn't pay for the watts link over the PHB (simply beef up the stock PHB setup). I would simply put my money elsewhere.
That said, the lakewood unit looks of the proper design. You want the pivot point attached to that chassis, as it is, and the axle brackets are probably sufficient. If it's rigid enough is another question...
Dan
P.S. You'll have to reroute the exhaust most likely as well, a pretty big downside.
I checked out the instructions on Lakewood's website and unless I missed it they say nothing about rerouting the exhaust. From the pictures in the manual the exhaust looks stock. I'm pretty sure it is just a bolt in installation. On the other hand the Saleen kit requires a special rear end cover.
I was just wondering if anyone had installed one. And what their impression of the Lakewood unit might be.
As far as which one is better PHB or Watts. The Watts link is superior for autocrossing/road racing. The PHB controls side to side movement of the rear end (which makes it superior to the old 4-link setup). But the pivot point for the panhard bar is on one side of the car, and it allows one side the axle to travel in an arc as it moves up and down. If I'm not mistaken this can alter the rear end alignment. On the other hand the Watts link controls side to side movement, but because the pivot point is centered on the center of the axle it allows both sides to move up and down equally. It makes for a better handling car.
For drag racing I don't know which would be better, but I suspect as oODanOo said the PHB might be better.
As far as everyday driving I don't know if it would make a difference.
From the thread you had a link to is sounds like you changed the rear springs but not the front. Is that correct? How is the ride height? I was kind of thinking about doing that. I don't want to lower the front as I already have occasional scraping problems on the awesome streets here, but I wouldn't mind dropping the rear some as long as it doesn't look funky. Do you have any pics?
The car evens out. The ride is marginally stiffer and the pinion angle remains in spec. But this is only using the Roush rear springs. Overall I like it. I'll keep it like this as long as the car is a daily driver. Once i get something else for the commute I'll drop the front as well. Gives you options but other then that it is still an excellent choice.
Excuse the darkness in the pics but that's how the car sits I'll need to get better shots.
I didn't get a chance to weigh it but it I can tell you that it definitely is heavier then your panhard setup. The way I see it the LCA's and the Springs are light weight that offsets a little for the increase. Besides it's not a bad thing to weigh down the back end more considering the car is nose heavy that brings the weight distribution more closer to neutral.