On my Oliver 1550 (which I no longer have), I'm thinking the hex headed plug on the right side, highest up, just under the seat, was the power beyond port. There would be a 3/8" threaded hole inside, which you plug, then the juice is diverted to the outside port. But I'd recommend getting a book to find out for sure. And I don't know what you do with the present hookup on the left side- but it almost looks as if the two sides are symmetrical, and you could use either side. If they look the same inside, I'm thinking you could switch the internal 3/8 plug from the left to the right, the outer 1/2 plug from the right to the left, and the hoses from the left to the right. Same with the return line. Clear as mud, right?
I'm curious about that big plug on the right front corner of the housing- anybody know what it is?