After reviewing the SDH article Gunflint Charlie mentioned above I see that he was correct in the Dickinson gun's use of standard V-type mainsprings instead of the bow type springs utilized in the Dickson, McNaughton and McKay round action trigger plate guns. I had read all the articles but somehow missed that.

I'm blaming my error on the little bitty exploded view picture in my Dickinson owner's manual. The three action walls on the trigger plate separating and enclosing the left and right locks looked to my tired old eyes like bow springs. If I keep learning more stuff like this every day I might know something 'fore long!...Geo