Pull gently on the PCB to make sure that it's not stuck to any of the standoffs where screws had been holding it

Press the wires from the output transformer and reverb as far away from the PCB and as close to the chassis as possible. The edge of the PCB will need to come down to the bottom of the amp where the tube PCB was before the pots will be able to clear the chassis

Using gentle pressure on the top of the board and making sure it's not getting hung up on any wires push it towards the back of the chassis( where the tube board was) until the pots have cleared the top of the chassis then pull the board up to you to expose the solder side of the board

DO NOT PUT ANY PRESSURE ON ANY COMPONENTS INCLUDING THE FILTER CAPS WHEN TRYING TO MOVE THE BOARD