I want to note that most of us don't know much about the 1550's...
I was also thinking that it could be a possible engine swap, BUT... the 1550 is a 4WD side by side,
According to the parts list that I have, (it's too large of a file to share on the forum)
they originally came with a gas Kawasaki FH680D V-twin gas engine, or a Kabota D722 3 cylinder diesel engine,
and I'll take a guess that both of them spin counter-clockwise, so it'd be kind of difficult to screw that up.
The manual shows a single shift cable, (it'd be impossible to reverse it at the shifter),
and then the cable goes to a bell crank on the transmission in the center of the vehicle.
Is it possible the the bell crank is installed incorrectly or upside down? I don't have a clue,
but I doubt that something inside the transmission is/was installed incorrectly.
However, I've been wrong before!