The mechanical advantage (MA) of a class 2 lever is the length of the long arm divided by the short arm. The eccentric in this case is the short arm. So for example, if the lever is 24" long and the eccentric is 0.5", then the MA is 48. So if you are pushing down with 10 lb force, the force on the die will be 10 lbs x 48 = 480 lb.
And yes, this would be easy to build and take up much less space than a hydraulic shop press modified for clicking. Other than the upper and lower plates, I likely have most of the parts required in my "junk box" (several bins). I have a 20 ton shop press, but it is an hour's drive away. Might have to think about this a bit more!
Tom