It seems there are 2 knobs one on either side of the lens, unscrew em and the board will come out as normal by pusihng it to the rear n it will drop down. If the board doesn't drop, take the 2 rear screws n that bracket off n the spring will fall out then the board can be removed.

My 4x5 Beseler has the same screw knobs on it's board.

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