So it looks like my 2003 6mt g35 engine has finally died. At least that is what my mechanic says. It cut off while I was driving and qould crank as if it was locked up. Any suggestions for places to order a goid engine? Suggestions on the year etc? Thanks in advance.

 

So, the engine stalled out on you, then when you tried to re-fire it, it seized up???
If the engine is absolutely D-O-N-E, good news is there are a ton of used VQ35de's. Not sure whereabouts you are located, but there are a few JDM engine suppliers on the west coast, and I imagine they are willing to ship. Typically the motors have 45k-65k claimed mileage.
For your question regarding the year, as I understand the non-revup VQ35de (*RWD engines*) are unchanged internally for USDM and JDM engines. Not 100% on that, so hopefully someone with more knowledge than I can chime in...

I do know that they changed the accessories/electronics a over the years, early-03 sedans have mechanical fans, and for whatever reason they kept the fan clutch pulley all the way up until mid-2006 (I have an 04 and removed mine, easy mod)
Also, mid model year 2004 they changed to wide-band upstream oxygen sensors (6 wire vs 4 wire harness).