Hi Greg
One of our Scott Bonnar guys should be able to give you a more indepth rundown on it.
I would personally keep the old engine in the shed, and put a new ohv briggs on - this will prevent any damage to the rails the engine sits on (the old engines cause bending and cracks)
The rails don't seem damaged, but take a few photos for us to look at of around the engine mounting bolts (with dirt removed) as some cracks may be appearing
They use a br2-lm plug
Regards
Tyler