My two cents worth
Benjamin Wilson's Diaglott had been part of the Bible Students references since the Russell days, and the Kingdom Interlinear is presented in a very similar way, almost an identical format as the Diaglott. My guess is that Fred Franz produced the Kingdom Interlinear pretty much on his own as he worked on the NT of the NWT. The OT, though was a different matter. The Bible Students did not ever have a Hebrew interlinear. In fact there are not a lot of them out there. I have one, (Jay Green ed.) and honestly it is not really helpful to a non-Hebrew reading student. It reads from right to left for one thing, and is really difficult to follow.
I concur that the possibility of the WT of producing a Hebrew interlinear is virtually zero.