Quoted from Schwaggs:HEP mounted that one in the non-stock position (floor of the cabinet for some reason) and therefore had to use a spring on the mech.
Your picture is the standard mech and location. No spring used when mounted in the stock position (vertical).
Yes the game I did was missing the assembly and my experience with the original style is that it is usually pretty weak.
That is why I took the opportunity to change it up.
Worked great.
https://pinside.com/pinball/forum/topic/hep-firepower-2018