@Ben ********
Basically, the whole process of visa and extension Non-O based on marriage is quite similar to Non-B process.
if you are on extension, you don't have to apply for the first visa (Non-O based on marriage). You can apply for just changing reason of extension proving two months seasoned fund.
If you are on the first 90days from Non-B visa, I think it's unlikely possible to change to Non-O in-country.