Stern / JJK Pinball Speaker System Upgrade Kit

Spike 2 Stern Pinball Speaker System Upgrade Kit includes:

• A pair of tweeter for back panel speakers
• A pair of mid woofer for back panel speakers
• A pair of crossover for back panel tweeter and mid woofer
• One piece of 8" cabinet woofer
• One piece of cabinet woofer crossover
• One pair of back panel speaker adapter for 4" speaker plate (Premium / Pro)
• One pair of back panel speaker adapter for 5.25" speaker plate (LE)
• One piece of cabinet woofer adapter
• Eight pieces of short wood screws to install back panel speakers onto adapters
• Eight pieces of long wood screws to install the cabinet woofer onto the adapter

Jersey Jack Pinball Speaker System Upgrade Kit includes:

• A pair of tweeter for back panel speakers
• A pair of mid woofer for back panel speakers
• A pair of crossover for back panel tweeter and mid woofer
• One piece of 8" cabinet woofer
• One piece of cabinet woofer crossover
• One piece of cabinet woofer adapter
• Eight pieces of long wood screws to install the cabinet woofer onto the adapter
• One piece of self laminate sound damping materials to attach to the mid-woofer enclosure (Cut it into four pieces) 

Stern's Installation instructions are here.  You can also see how this project was designed from the beginning on the Pinside thread.  Pin-Tweak at Pinside has provided his installation experience here.