I think Americans are exempt from the police certificate thing. At least thats my impression...
Also, I don't live there anymore, but I used to live in central California. I'll be in Maun by the 10th of January. I'm also in the same boat as you, with 1400 hours. All though from what I read, having a lot of time really doesn't get you any further, as they don't really seem to care about how many hours you have.