Hi Chris,

It will be worthwhile doing some pre-reading on your engine before you go much further.

Here is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/flivAJX-nfBhU7y.pdf

Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6ntABVJ1DajI.pdf

The vibration you are feeling in the handlebars is not a good thing. It is most likely due to your cracked chassis rail allowing the engine to move up and down in a fashion that will further damage the rail, and may damage the clutch or the bearing on the engine output shaft. I suggest you refrain from using the mower until the chassis is repaired.

I also suggest that you carefully read this thread:
https://www.outdoorking-forum.com.au/forum/u...mp;Words=crack&Search=true#Post48231

Your machine came to you at a very good price, especially for WA, where prices for second-hand reel mowers are very high. It may be that the low price was for a good reason, and that reason may have been related to the condition of one or both chassis rails. This is not a fatal fault in the SB45, unless you are over-charged for repairing it, but it is a very serious condition and needs to be dealt with properly, as explained in the thread above.