You may clarify if this 90 deg you cannot achieve is in the direction the spindle travels or you are talking about the other direction, that is inline with material feed.
I have a diff Felder machine but achieving 90 in the direction of spindle travel is done by a set screw. If the screw is already bottomed out than you may need a screw with shorter head. You may also have dust preventing the last bit of travel.
If you are talking about not achieving 90 in the material feed direction, that is more complicated. I can only hazard a guess that the entire spindle assembly would need to be shimmed against the base machine. I have never looked at this adjustment on my machine, so not sure if it is even possible.
imran