U.S. Engine Inc.
 

Has anyone used a rebuilt motor from this company. I like their prices and warranty:

http://usengine.us/mercruiser.html

I would ask the tech department (not a salesman) for camshaft duration specs @ .050 lift and the configuration of the piston tops: flat top, dished, or quench.
If they can give a good answer to these questions I would think that they have some experience with marine engines. If not I would assume they are automotive rebuilders selling a marine version of an automotive engine.
Buying a rebuilt engine is not bad if it includes new rocker arms, pushrods and valve springs (can't use new junk either). These parts are not critical for a slow speed automotive/truck engine but very critical for a high rpm marine engine.The most important part of any rebuilt engine is the valve guide clearance and the precision/tolerance between the valves and the valve seats.
Good Luck
Dennis Moore