1997 Centurion Elite bow rider worth and engine replacement

First of all does anybody have any idea what a 97 Centurion Elite bowrider(direct drive) would be worth if it had a brand new engine and was in decent shape/clean? The boat has a monster tower, rankin cover, 2 or 3 amps, tandem trailer.

Also, how hard is it to replace an engine block? I probably could find access to a engine lift to get it out and put it back in. Is it pretty much as simple as swapping the manifolds, valve covers, distributor, sensors/switches, raw water pump, etc.... over?