Output transformer for GA-1RT

[67supertrem]

I'm looking for wiring information for a Gibson output transformer.

Transformer is marked GA5-0, 174A7, 549-6118

Wires:

1 Red
1 Blue
2 Green, (I supect these could be speaker outputs?).
2 Black ( Possibly grounds?).

I am assuming the speaker outputs should be 8 ohms?

Any information to confirm would be apprecated.

Thanks ST