17 is spec for 95-99 Phase 1 and will work here for your Phase II 99
the FSM from Subaru is free all over the internet for that car. Get that and work off of it. There’s an angle reference for the pigtail they want to retain as well
The numbers referenced are so close that theyll fall within the +/- range and average tools in old threads won’t be accurate anyway. Unless it’s freshly chased and cleaned block side threads and a new bolt, using lube, and a really good torque wrench that has been calibrated recently, and the angle of access and extensions/adapter interfaces aren’t reducing that number.....it’s not going to be exact anyway within the small range of those numbers posted. Do 18 and call it a day.