bulkheadhelp

I recently purchased a 1973 E25 that I am working to bring back up to respectable condition. One of the issues is replacement of the aft bulkheads where the chain plates attach. The port was easy to remove and use for a pattern. However, it appears the only way to replace the other is to cut it...

I must replace the 1/2 inch thick plywood bulkhead on the port side of the cabin, 1979 E23, fixed keel model. Can the existing bulkhead be removed in one piece and a new one installed without removing the mast post? Any advice or shared experience will be greatly appreciated. pmk Dallas Tx