Hi Padman, and a warm welcome to the OutdoorKing forum.It's great to welcome another Scott Bonnar owner aboard. grin
So that we may help you with you questions, could you please post a pic of your machine, form different angles, including one of the ID plate affixed to the mower, as of the sprockets the chain connects to....This lets us correctly identify the model and gives us an idea how to proceed.

I believe yours to be a Model 19, first introduced in 1953, finding a new or even a second-hand grass-box for it may prove a challenge...and spare parts maybe a bit thin on the ground... frown
But please post the pics and we'll see what we can do. wink
Once again, :welcome:
cheers2

Please do not PM me asking for support. Please post your questions in the appropriate forums, as the replies it may receive may help all members, not just the individual member.
Kindest Regards, Darryl grin