I'm 99.9% 3.5" is correct. I was told 4" was what I needed but I'm pretty sure my rusty old Wico's are 100% original and they feel "just the right height". I was told by several collectors that they were 4" just like Robotron but you have to remember that Robotron has wood behind the metal CP.
Van knows the creator so maybe she can ask him for sure.