[Bruce Edwards]

First off I see no way that a 850 could be to large for a built 460 style engine. Get the model number of the carb and check the jet size. I would pull the carb after a short start up and check for fuel running out of the bottom in the area of the power valve bleed hole.
Some cabs are set for different things. If your carb is set up for a blown motor it will be to rich for your set up.