Help figuring out if this Mark III was modded by Mike?

[frontline205]

Hi don’t know if you guys can help with this but I got a Mesa Mark III amp. And I’m trying to figure out if it was modded by Mesa or someone else and what mod is it. I see the R2 mod sticker and a + with MB but maybe the plus was added later? I called Mesa and they said it’s not in their recent records. The person I bought it from said it was sent to Mesa but doesn’t know what was done to it as it was by the previous owner.
Here are some pics if anyone knows anything. Is there a place inside the chassis I should look?