Hi xhall,
Being that it is the rare 450511 model I would repair it. Hands down.
Which twit put the reel bearing shield on backwards !! Everything's there all it needs is for someone to take a step backwards and say to themselves, hey this isn't all that hard.
Once all the crappy paintwork is stripped off and all the components are reworked it will be a great mower again.
If you were in Adelaide I'd take it off your hands.
Cheers,
BB
BTW I'd say it is the original engine being made on the 18 of July 1974, thus making the mower around November 1974 which is towards the very last of the 14 inch model.