Need help identifying engine...

Hi, I have a 1976 911 Targa but I don’t think it has the original engine.  The engine number is 6640261.  All I have been able to salvage from this number is that the first indicates it's a 6 cylinder and the third indicates it was from a 1974.  I'm unsure what the second digit represents.  Can any one help or give me a reference as to where I can find this information?  Thanks!!
 

Brian
 

I also found the number 911/83 on the motor.  I think this is the 2.7?  Would 911/83 signify Carrera?

That number is showing just out of range from my sources.  Closest it comes to is a 74 motor, which is a 2.7L.  What makes you think it is not the original motor?  Can you take some pictures of the engine from above and below for me?

Never mind, I found it.  I dont know if it is the original motor that came with the car, but it is the same 2.7L engine that came with the car new (you dont know if they had a motor fail and swapped in a motor out of another 74.....It was produced between 1973 and 74. 

Thanks, I appreciate you checking out the numbers for me.  Here is my dilemma;  I live in CA and need to smog the 911.  When I took it to the shop the guy said something wasn't right because it didn't have the proper "hook-ups" or equipment necessary to install smog equipment.  He said he didn't believe it was the original engine and wanted me to get the year and specs.  Well, after doing some research I guess it's a 1974 motor and it is still the 2.7.  However, according to the 911/83 it's a Carrera RS engine.  If you wouldn't mind double checking this I would appreciate it. This would also make since because the 1974 Carrera RS engine didn't come with the proper emissions equipment for CA and wasn't able to get smogged here.  I guess the 911/83 engine's are the EURO SPEC 2.7's and are somewhat hard to come by today.   Here is another thing that doesn't make much since though....I looked at the RS 2.7's and it doesn't resemble my engine.  The intake manifolds appear significantly different (I don’t know if this was interchangeable).  Any information you could give me regarding my questions would be much appreciated.  THANKS!
 
 
P.S.  I have attached pictures of my engine (RED) vs. the 911/83 Carrera RS engine (YELLOW)....    
 


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No, 911/77 is the Carrera RS with engine serials from 66400001-6640200

Isn’t the 911/77 the Carrera RS 3.0L engine?  I was referencing the Carrera 2.7L 911/83 RS engine.