Rebuilt mine about a year ago, Is it imposable - no, likely not going to happen though.
The Cam does remove from the front , there are bolts under the gear that keep it in place, the problem is that you will need to remover the rocker assembly, pull the valve push rods and lift
all of the lifters as high as they will go to clear the cam, next you will need to drop the pan and remove the oil
pump as it is geared to the cam, going to need a lot of room to do this as you will be working on the top and bottom of the engine
You might be able to do it on the boat by pulling the engine from the mounts and working on it in the salon