Can you not unbolt it and count the teeth? I'm guessing it's in the car right?
I looked and didn't find 1 that has a sensor in the front. I think the ones I saw were all Z32 with 2 on the rear cover.
When used with fuel injection, the Davis can pull fuel or manage a DBW throttle.
As for the 7531, I've been around them, in my opinon, not a great solution for a street/road race car.