The Mitsubishi M5128A is just another jellybean sort of opamp that can be used in most any pedal circuit that calls for a dual opamp. They are no longer in production and came in two package styles - DIP-8 and SIP-8. And IIRC, Boss used the SIP-8 packaging in several of their pedals in the beginning. The DIP-8 packaging of the M5128A has the same pinout of several other dual opamps like the 4558, TL072, 1458, and so forth. IF you have the SIP-8 packaged M5128A opamps, you will need the datasheet to see the pinout.