Were the fuel rails cleaned out before replacing that compressor? What happened to that compressor to cause it to fail? If the compressor blew, it could have blown chunks in the fuel rail which in turn debris gets into the injectors. If that compressor was replaced and the fuel rails were not cleaned, then the residual debris got to your injectors. If you're reusing the fuel rails and injectors after the rebuild, make sure that you clean them or you'll risk blowing up the rebuild.

What are the warranty options on the rebuilds? The new Merc block seems the way to go providing that ALL steps were taken to install it.

Good luck!