I've been looking at the new changes to Caesar and hearing a lot about the FEA Tools program. I had a question regarding how Caesar 2 calculates the SIFs in the new 2017 version 9.0. Does CAESAR II use the calculations from B31J or STP-PT-073 to calculate SIFs?

I'm trying to determine if I would be justified in purchasing the 2 standards in order to improve my stress analysis practices before looking at bringing up FEA Tools with my company.

CAESAR II does not directly reference B31J or STP-PT-073. The program collects the B31J numbers from FEATools.
STP-PT-073 was the ASME research project behind the re-alignment of SIFs between B31 Code Books. That work was incorporated into the new B31J. This new B31J is still out for public review. Once public review ends (next week), ASME can elect to publish it or not publish it.