take the gasket off the threaded tube, I can see the corners of the hex head peeking out above it. Deep socket over the tube and unscrew. There is a big gasket under the sheet metal plate, and I think a small one that goes over the threaded tube behind the sheet metal plate and the one that is on the threaded shaft on the outside of the sheet metal plate. When you reinstall the threaded shaft be sure you clean the female threads that go in the block and use sealer (all this is under pressure). Did I miss anything? A lot of a-bodies came with the 90 degree adapter for exhaust clearance and room to get a large (PH8A) sized oil filter in and out. This would be the time to change if you need it... pulling the engine to change the filter would be inconvenient.