1973 Duster 340 Clone, Whats it Worth

The "-3" is the casting core box number. It has nothing to do with quality - the factory didn't care that much. The fact that it's a lower numbe tells me it might be an earlier block/engine - bbut you have to look at the stampings to know for sure. Check the casting date on the pass side of the block too.
I agree with Joe - it's a bastard, and looking at the pics it's a quickie paint job. They didn't spray the engine aby, and the panels are not aligned very well at all, there's filler in the driver's rocker too. Personally at best that's a $6-7K car to me.