Did the previous owner mention why the engine was rebuilt? The 2.6 is very sensitive to being overheated - if your cooling system isn't functioning properly you will very likely blow a head gasket and/or crack the head. If the rebuilder used new gaskets and seals on the motor but didn't use any RTV at the corners of the rear semi-circular plug, that's more than likely the source of your leak.

Why do you feel that the alternator is on it's way out? I'd be doing a little more diagnosis before throwing a new alternator at it - are the battery terminal connections clean and tight? Is there corrosion in the cables themselves? Is the engine ground cable attached and making good electrical contact? Is the alternator belt tight? If the 'rebuilder" had the engine out of the vehicle then there's a good possibility of several of those issues being a problem rather than a failing alternator.