There is some misinformation in this thread.
First, the engine shown on the scooter in the original post is a Briggs & Stratton, but it is not an NP. There were many engines at about that time that were similar in looks, bore, stroke, hp rating, etc. And it was not terribly uncommon for the original NP engines to be swaped with 1950s Briggs engines after the kids those days blew them up or ran them out of oil. Your model would have left the factory with an NP.
The Clinton engine (710aslb) was used on 750-1000 of the first production run scooters. Thats generally believed o have been in 1946, but since Doodlebugs don't really have years, nobody knows.
The 1046 number is meaningless...it is not some kind of date code. It is strange they used it as a "type" number, as no other scooter was ever built by Beam Manufacturing.
The C designation is the model number.
I know this thread is basically dead and the machine has been sold, but I can't help myself...if you've got one of these great machines or happen to run across one please understand that they are essentially antiques and they are rare and valuable. It is my opinion that they should remain as original as possible. Sure, it would be your machine to do what you want with, but keep in mind there are plenty of collectors out here that appreciate these machines that will restore them that would be happy to buy your projects. And, if you're lucky enough to have a fairly complete machine, don't part it out, sell it whole.
You can read much more of what I've written on Doodle Bug scooters by running a google search for "aaca Doodle Bug." I've posted quite a bit of detailed technical and restoration information there.