notched transom OR jackplate ?

[pancake]

Ok i have a 1984 20 Fisherman with a 2001 150 hpdi yamaha currently installed on a 20" notched transom . I wanted to raise the motor with a manual CMC jackplate but it looks like i may have steering cable issues, so is the best way to get the 5 " increase i need to get the motor out of the salt water is to fill in the notch area which would increase its height 5".

Can someone tell me how you can fill in the notched area? Do i have to rebuild the transom with new plywood?