Quoted from GSones:

I think that the rubber push-on style of plastic retainers is the correct style for this era of Bally. I also like this style as they are quick and easy to remove and the rubber will allow the plastic to "flex" a bit as opposed to coming up against a hard nut.
I personally prefer the look of whatever was original to the games. While I hate the aggravation of taking off the Palnuts on Gottlieb games (using the Palnut removal wrench helps tremendously), the chrome nuts look best and most appropriate to me.