Can you give us the model number of the engine? If it is an overhead valve check the valve clearances and adjust if needed.
The starter and alternator will be separate units and expensive to replace so do some troubleshooting first.

It's a Briggs 14.5 HP OHV Model unknown at this point.

The charging coil is underneath the flywheel, since the starter stops turning when you release the key. My guess would be fuel. To check this, either spray or pour a small amount of gas into the carb. If it doesn't fire, I would next check for spark.

Adjust the valves!
There are numerous posts in the TRACTOR forum about Briggs OHV engines being difficult to crank over.

At least you haven't replaced the starter motor & solenoid too, which are usually steps 2 & 3 the poster does when a valve adjustment was all that's necessary.

IF the valve lash gets too excessive, the compression release doesn't work!

Thanks Bill and Canguy.
The engine will slowly turn over, but not fast enough to actually start it. It sounds as if a valve adjustment is in order. I'll go look in the tractor forum to see if I can find one of those posts!

Thanks guys!
I adjusted the valves as recommended to 4/1000 of an inch and she starts and runs great now! Thanks again for steering me in the right direction!

Here is a link that might be useful: Smalleng.com

I bought a used Murray 42" 20HP riding Mower and it came with a 40" MTD Snow Thrower attachment with braces belts etc. would you know what the part # for this is, or how I could get a site to download assembly instructions.
Or if it's even interchangable with the Murray Mower.
Thanks