1910.178(q)(6) Below is the most direct law that would apply to keeping the operator's manual in the designated holder supplied by the manufacturer on the machine. OSHA has said in the past operator's manuals should always be available to any operator when needed. The federal law below applies because operator's manuals are always shipped from the manufacturer with the manual in the designated pouch, carrier or pocket usually decaled or labeled as such on the truck. You can't eliminate any parts (operator's manual) off the truck.
1910.178(q)(6)
Industrial trucks shall not be altered so that the relative positions of the various parts are
different from what they were when originally received from the manufacturer, nor shall they be altered either by the addition of extra parts not provided by the manufacturer or by the elimination of any parts, except as provided in paragraph (q)(12) of this section. Additional counterweighting of fork trucks shall not be done unless approved by the truck manufacturer.