I'd say dont be intimidated by the idea of using 20-24v to actuate things, you get snappier response and it'll use 1/2 the amount of current than same being fed 12v. some of the larger solenoids you can find at Amazon (10mm throw) may do things you want, some are confusing about push vs pull, makes shopping kinda "fun" but they arent too spendy. pop bumpers from scratch might be a real headache, maybe lots easier to shorten the height of full size units 1/4" so they'll hit the smaller 3/4" ball. cruder but easier than that is gear-motor driven spin bumpers, nowhere near as nice, they'll take up a lot less space for the small playfield area. action-hit determined by rpm and torque delivered with voltage and gear ratio. direct drive ones in most toy machines get about stopped with the first hit, and slap the ball ridiculously fast when. something 6 or 10 probably a lot more consistent-powerful, changing spin direction easy as swapping 2 wires, or could be manipulated with a target switch(es?).