I agree with all that was said above for the most part however there have been tons of Effies and first series chev trucks with Camaro clips that when done right is an OK set up. As far as the weight of the vehicle those two are very close to each other. The average Camaro weighs 3600 and the average F100 is around 3700.
Using the Clip; As mentioned above, I do not like Z ing the frame. True it has been done and you will talk to guys who have done who have tens of thousands of miles on them... doing it in this day and age with the availability of aftermarket parts, it is a band aid and in reality may not save you much money by the time you get done prepping the sub, rebuilding bushings, brakes, bearings ect. What you have to pay attention to in using that piece is where that front suspension was engineered to be at ride height from GM. You have a couple of inches on the lowering side where you are safe however if you try to take it too far out of its engineered height then your geomrety is going to be out to lunch and the truck will have serious handling problems. Also keep in mind that if you are looking at that subframe with it laying on the ground with the springs still in it and no weight on it; it is way above what factory ride height is intended to be. I actually see alot more of these trucks where the front sub was installed at this max extended height then when they actually get the weight of the vehicle down on it, it has actually gone way to low and they are trying to pick it up higher.
The use of an aftermarket crossmemeber; If you purchased one of these from a reputable shop you can be rest assured they have already done their homework on the geometry and it will designed for your truck to sit where you want it ... not to mention that you will be upgrading your brakes, steering and better overall geometry to boot.