The Kingdom Interlinear Translation of the Greek Scriptures 1969 is available online for free.
In the foreword, on page 9 we see the greek text that is the basis of the New World translation is the 1881 Westcott and Hort text (same as was used for the Revised Version of 1885, the ESV, ASV, NIV, etc ). They also use the Nestle’s greek text that is the text used by most all of the modern translations including NASB, NIV, HCSB, NET, RSV, TNIV, etc.
It is little wonder why so many of the modern translations agree with the NWT, they are using the same source texts.