I don't see specific requirements if you already have Rotorcraft Category rating what is required to add the Class rating. Just proficiency and a sign off for the test?
From your first link - Upon successful completion of this, a logbook endorsement will allow you to operate within this category as a Gyroplane Sport Pilot.
So that only applies to adding a Sport Pilot Gyroplane rating. If you want to do your PPL or CPL, you need to follow 61.69, which requires a checkride with a DPE The following ii if you already have a Rotocraft Category rating. Without a Rotorcraft rating, you need to meet the Aeronautical Experience requirements in 61.125.
c) Additional aircraft class rating. A person who applies for an additional class rating on a pilot certificate:
(1) Must have a logbook or training record endorsement from an authorized instructor attesting that the person was found competent in the appropriate aeronautical knowledge areas and proficient in the appropriate areas of operation.
(2) Must pass the practical test.
(3) Need not meet the specified training time requirements prescribed by this part that apply to the pilot certificate for the aircraft class rating sought; unless, the person only holds a lighter-than-air category rating with a balloon class rating and is seeking an airship class rating, then that person must receive the specified training time requirements and possess the appropriate aeronautical experience.
(4) Need not take an additional knowledge test, provided the applicant holds an airplane, rotorcraft, powered-lift, weight-shift-control aircraft, powered parachute, or airship rating at that pilot certificate level.