70 Swinger over center clutch spring

I saw some discussions about the over center spring. I do not have one, and my pedal is "VERY" hard to push. I do not know what type of pressure plate I have [just got car in Sept. last year ]
I am not real smart with cars , but I do not understand why a diaphragm pressure plate, is not suppose to have the spring. I would think the pedal stroke would be the same, with or without the over center spring. The clutch seems to disengage without a long push, maybe halfway to floor, but of course , you can push it to the floor. The guy who just painted my car also noted the very hard push. I did see this neat trick to help to install spring. What am I not understanding about this spring thing ?
Dodge 6 11 2022.jpg clutch spring trick.jpg