Custom II, III and similar
Loosen set screw on right hand side
Move carriage to left, and stand machine up on its back side
Loosen set screw underneath left knob. Turn knob until you can see the screw from underneath.
Pull left knob to remove it
Now pull right hand knob, and entire platen rod should pull out that end
Move carriage to right
Gently lift right end of platen and pull up and out to the right