I agree with Pinhead, I would add another lower current coil that triggers off a new switch added to the pop bumper relay switches. This would also let you add a separate fuse to the topper if you desire.
With the extra switch on the pop bumper relay switch stack you then don’t have to use a DC coil with a diode, you can run the Tommy Gun coil off one of the AC power rails.
One more suggestion, if this is for a topper, and you want to run it off a pop bumper, you would then need to run wires (and a connector) from the playfield up to the head. What if instead you triggered off one of the point scoring relays which are already in the head, making the topper installation perhaps less involved?
Love the idea, BTW
Alberto