The Mark III Musician was a later model, it had the five input jacks in a group on the left. The preamp was based on ICs.
The Musician - plain old Musician - came first. I have drawings for the 200, 300, and 400 series of Musician. If I have them, Peavey has them.
The 200 was basic, hi/lo pair input jacks. Fuzz, trem. Schematic calls for a "to reverb drive" but includes no reverb circuitry. I don;t recall if the amp had reverb or not.
The 300 series was a little fancier, same hi/lo input jacks. It shows a reverb as well as the fuzz and trem. Also has the Spectrum selector switch.
The 400 series is like a grown up 300. Same hi/lo inputs, plus reverb/trem/fuzz
But there is also a Musician B-series, and I believe that is what Cereal has. Got the hi/lo jacks for each channel PLUS the series and parallel jacks. Fuzz/trem/reverb too. AND it has the five-button stomp switch.
Ask Peavey for the "Musician B-series" schematic. I don't have mine scanned. It covers the preamp, ie. the front panel. You will have to determine which power amp is used, ie. the rear panel.