Not knowing any details, best answer is "maybe"
Would help to know the following:
Current Pontoon size, log size, etc
Current motor size
Gull details of current issues you mentioned on steering
If the core plugs were pushed out, 99.99995% chance the block is cracked. (GM blocks never survive a freezing that pushes core plugs out)
Take it to your local machine shop and have it magnafluxed
Without knowing where you are at with your boat and current prop, no one can make a guess if you have the right prop or the wrong prop
The right prop will allow your motor to hit the top of the full RPM spec lightly loaded
You never want to be over-prop'd
