Welcome, fellow Mark III owner/operator.
What exceedingly good taste you have, sir.
The switch for Simul-Class will be on the far right of the rear chassis next to the cooling fins, or it's on the front panel. No switch means no Simul-Class.
If you have only two power tubes, you don't have a Simul-Class amp. No biggie.
The "MB" initials belong to Mike Bendinelli, who did the final test.
The manual is available at the Mesa website, and has many setting suggestions.
To start, you might try:
Volume - 7
Treble - 7
Bass - 3
Middle - 5
Everything else to taste.
Mark IIIs have a 3-spring reverb, which is more diffuse than the "regular" 2-spring we're all familiar with from classic Fender amps.
The number on the reverb tank is "9AB2A1B". If you replace it with a tank with the designation "4AB2A1B", you'll get more a more obvious, crashy kind of reverb.
Seacrest out!