We would not recommend doing this but if it is a single door header you can physically cut it down. Just make sure the end that is cut is the control box end not the motor end and minimum it should be cut down to is 33” as that is how much room is needed for the motor and control box to fit in header. Also, you will need to drill and tap for the screws on the end of the filler plate as those will be cut off when you trim the filler plate down to the proper length.
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