Hi Jen, welcome to Outdoorking.

That is a serious crack in your new SB45's front frame rail. At this point I do not know whether it has been repaired from underneath the hollow rail. If it has not, it will need to be repaired before you can use the mower - it is not safe to use it in that condition.

There is no reason you cannot get the engine going yourself if we go through the process together carefully. You may run out of patience or determination along the way - I cannot predict that, and wouldn't if I could, but if you stick to it, the job is doable.

As a beginning, here is the Operating and Mainteance Instructions for your mower's engine, which you can download free from here:
http://bsintek.basco.com/BriggsDocumentDisplay/lrvvA-wU7eL7hAxB91ObQ.pdf

Here is the Illustrated Parts List, also a free download:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6jmvGVJ1DajI.pdf

The engine was made on the 18th of June 1973, and is most likely the original engine fitted to your engine in the Scott Bonnar factory in Thebarton, a suburb of Adelaide. That would mean your mower was probably manufactured at about the end of 1973. Our Scott Bonnar guru Deejay will tell you more about the mower when he can, but he is involved in some family matters at present and is focused on those.

I suggest that you read the Operating Instructions first, that will help you to get focused on how to look after the engine after you get it going. The Illustrated Parts List (IPL) will be referred to repeatedly as we move forward with this, along with the Briggs and Stratton Service and Repair Instructions 1984, which you can view free page by page here:
http://recoveryvehicles.tpub.com/TM-5-4240-501-14P/css/TM-5-4240-501-14P_78.htm

It is a very long book - a couple of hundred pages - and I will help you find the right page each time we need it.

For the present, I suggest that you read the above operating instructions, then remove the vertical screw in the top of the air cleaner and post a picture of the urethane foam filter element you will find under the top cover. It may have become completely soaked in oil due to the mower being laid down in transit.