Why are you trying to remove the shaft if you need to replace the prop?
Throw the 2x4 away before you destroy the fairing. If the shaft is that badly stuck you will NEVER get it off while in the water.
If it is a prop replacement as your posting suggests, then you can easily do it in the water with a mask and snorkel.
Remove the nylon bolts from the hub, you will find it easier to line up the replacement prop with two stainless steel bolts which will allow you to insert the nylon bolts in the remaining holes. Remove the two stainless steel bolts and insert the last two nylon bolts and you should be finished.
If your shaft is really badly stuck and has not be removed for a very long time, it most likely will need some heat after you have removed the entire assembly from the boat.