Should be. There are five drain plugs on a PCM 351. One for each riser, one aft on the left side of block, one forward on the right side of block, and one at the bottom of the J tube (between raw water pump and main water pump). If you're lucky (I haven't been so far) your boat will have been regularly winterized in the past, and you'll have an easy time getting your plugs out. My boat was a garaged SF bay area boat, and I'm pretty sure they never winterized it.
I've had both riser plugs disintegrate on me during removal so far
Luckily they disintegrated so badly that getting the remains out, while tedious, has not been terribly hard, aside from the terrible contortions I've had to put myself in to see what I'm doing lol.