Stay with the 2" flips, and, (as the picture above shows), have the rebounds below the flipper tips extend beyond the actual flipper. This is the "Liberal" setting on the machine. Mine is set up this way and I feel it's needed to keep the game fun. The center drop hole is really not intrusive, in fact you'll find you can never seem to get it when lit for special.
The game is all about hitting the side targets as often as you can. It's also imperative to land in 1 of the 2 rollovers at the top as you enter the playfield to eventually reach the hole special. Mine must be dialed in pretty good as I get there maybe once every 5-10 games, and when you do happen to get the drop hole when lit, hearing that knocker banging loudly multiple times, you actually feel like you DON'T need to play one more, (Ha).
I'll venture to say Slick Chick and King of Diamonds are the 2 best from Gottlieb in the '60's.