If the low side is stopping at X.055, the high side must be stopping as high
as 590
If yes:

You may have to physically loosen the dial disk shaft screw and "Walk it" to
get the spread center.
Then go to X.000 (this worked on my 301 with the TRW) and use the trimmer
cap to "pull down" to X.000.
If you like mark the shaft befor moving it

See if that works if not you have to operate, I never had to open the PTO on
the SBXX1 series.
Its a simple enough try

-Joe