Oh, yikes, a toroidal OT! One thing I've seen about toroidals, they have terrible overload characteristics. To be avoided in guitar/bass amps. In any case, if you believe black is common/ground, and you have green already soldered to the output jack's + terminal, then use any handy load resistor, send a sine wave thru the amp, dial up a low output just a volt or so on your green lead. Measure the voltage on your other leads, and that should help you sort out which is which as far as 2 - 4 - 8. If the previous tech had it "wired for 16" and there's no 16 ohm output, then it's likely he was using the 8 ohm output to drive 16, "close enough for rock'n'roll." Once you know which OT lead is which, you can wire the speaker jacks or put in a switch so the amp can be used appropriately.