Don't forget the red box, which you could make by replacing the 3.579545 MHz crystal powering the chip that the OP reverse engineered with a 6.5536MHz one, and

Don't forget the red box, which you could make by replacing the 3.579545 MHz crystal powering the chip that the OP reverse engineered with a 6.5536MHz one, and then the top row and bottom column tones become 1700 / 2200Hz to simulate the pay phone nickel / dime / quarter tones.