Seat Shock For 1969 Chopper Mini Bike?

I'm looking to restore what I believe to be a 1969 Bird Chopper mini bike. I'm having trouble finding the right shock for the seat and the right type of seat for the bike if the seat needs to be specific. Does anyone know what it is and able to help me out. I have a picture of the brochure of the bike its the one that looks more like a chopper(lower middle one)style. I hope someone knows what it is or if its generally a universal size.