Hi Steve and a warm welcome to the forum. Its always great to have another Model 45 owner on board.
Grumpy (our resident Briggs and Stratton guru) will give you advice on your engine probs and can date the engine for you.
Your machine is virtually the same as the Scott Bonnar Model 45 (late model) and all spare parts are still available.
If you can take some pics of the machine from different angles and a couple of the chain case (cover removed) and of the exposed areas of the sprockets (ie. not covered by the chain, so as we can see the condition of the sprockets. Also a pic of the cylinder reel and the bottom knife blade (also called 'the bedknife') so as we can assess the condition.
You mention that it is cutting lower on one side; this could be an alignment problem...see the post that we have just been discussing...Click
HERE Re: the cracked chassis rail...it needs to be welded or preferably replaced...it is just steel 'C' channel and could easily prefabricated and welded back into position. You would need to remove the engine to do so, and we can step you through the procedure when the time comes.
When we see the pics of the cylinder reel and bedknife we will tell you if it needs sharpening...there is a video in the Scott Bonnar topic on how to remove/replace the reel.
Once again, Steve,
