There is likely to be a way of zeroing the trim guages. I had a similar problem when running a pair of Yamaha 50G engines. On consulting the manual detailed information explained how to reset the guage by lifting the engine/taking the weight off the hydraulics and then manually pushing the ram back. It worked and was a simple operation.
Have a look in your manual, it may be similar - alot of these engines come out of the same factory anyway,
Cheers
Lester