Not sure, but you may get faster help by calling a Ford dealership and asking them what that part number is for.
Hopefully someone will post an answer for you.
Good luck.
I'm on the opposite end of the same problem.
I have a '90 stock flywheel that I was going to put back into the car in preparation to sell it, I'm keeping my billet steel flywheel, motosport clutch and lakewood bellhousing for the next project.
There seems to be some confusion on the 50oz / 28oz change, some say 50oz 157 tooth is late model, some say the 28oz is late model.
I only know one thing at this point, 164 tooth is old, 157 tooth is new.
Here are the casting and stamping numbers from my '90 flywheel, which is 13.25" diameter.
Does anyone have one of these in good shape (no heat cracks!) they'd like to sell?
Casting number : RF-E1ZR6380-AZA
Stamped number : E6ZR-AA 012 BL