I guess NT category stands for nomadic tribes and you come under OBC Category at a National Level. There is no NT a category for AIIMS admission.

Now marks. See marks is a very vague parameter to judge admission in AIIMS. It changes yearly and even in accordance to shifts-morning or afternoon. During my year of admission at AIIMS 2016, I heard the top ranked was 136 marks for morning and 128 for evening if I remember correctly. So a 140-150+ score is a safe mark. Percentile is a better predictor and for Delhi you need to have greater than 99.3 percentile.

Reference books = There is nothing special for AIIMS. All you need to do is be more conceptual in learning rather than facts and solve questions of JEE Mains level.