I know its the wrong season but while at the goodwill, I bought an engine for my MTD snow blower.

Its a 5hp Snow King complete with the electric start and is the same engine as mine except mine doesn't have the electric start. It was rebuilt, has the rebuild tags and everything. Got it for 39 dollars. I figure I did okay.

However this engine has the PTO shaft on it next tot he main output shaft.

What is that PTO shaft actually for?

well its not really the same engine, its a different spec then your original. some of the snow king engines on certain snow blowers use 2 pto drives one for traction the other for the blower system. not sure if this will work right for your application.someone else here may have more knowledge of the 2 different specs and if it will work for you. I dont have to many of these come through my shop.

some of the older snow king motors used the main PTO for the auger, and used the other PTO (which is actually the camshaft) for the drive belt

you could probably take the cam and sump cover off the engine you have already and put it on the engine you just bought and be just fine.