The Yanmars in J30s did change during the production run. So, there may be differences in the location and number of zincs. I have hull #359 produced in 1981 (commisioned in '82). My Yanmar 2GM has one zinc on the aft side of the cylinder head and one zinc on the starboard side of the block. The zinc on the head is mounted on a plate that is fastened to the head by 4 bolts. This one is relatively easy to remove. The zinc on the block is threaded into the block and needs a large socket to remove. I had lots of trouble with this one. The method that ended up working was to place a piece of wood on the side of the quarter berth (cushion removed), get a big socket with extension and ratchet, rest the head of the ratchet on the block of wood, put my back against the underside of the deck above and push hard. This method does provide for lots of leverage. If you have a breaker bar (hollow tube) you can slide that over the ratchet handle for more leverage.
Good Luck.
