Leave it in...
Unless you really need the space. I don't think it is possible to remove without cutting some fiberglass. I don't know of any documents or manuals for your project, but I know that if you buy an outboard motor from a dealer, they will mount it for you. But, I'd look for a used one first.Don't cut a hole in the transom to mount the outboard like the factory OB boats. If you mount it on a bracket attached to the transom you will be fine. Get one that has remote control and electric start. You don't really need a tiller. A late model 2 stroke tohatsu 9.9 with remote and electric will be around $1200. A good place to check is boat dealerships that take units in trade. Mine came off one of those MacGreger 26x things that are supposed to be comination sailboats and powerboats. (BTW, They are neither!) The owner wanted to upgrade to a 50 HP, so he traded in to the dealer. I got it for 850 from the dealer because it didn't have a tiller.... for a better idea of new motor costs, go to www.outboardsales.com