If the cutout in the deck
is large enough to accommodate the passing of the motor
and the bolts are removed you should be able to lift
it straight up. There may be a lot of sealer (which there should be) under the base holding it down.
Try taking a hacksaw blade and grinding the sides off the teeth (the set, so it doesn't scratch the deck) and slide it under the edge that seems to be the thickest, and start seesawing your way around the base. Wrap one end with tape to make it EZ on the hand.
Get what you can, lifting up occasionally to see if it will pry loose the rest of the way. Also you can use a small pry bar with a metal plate against the deck where you've used the blade.
Another method is using a piece of music
wire. But it takes two people working together. Force one end of the wire under the base until it comes thru on the inside and have the other person pull, while you can pull the other way, seesawing it back and forth cutting thru the sealer. It takes teamwork.