Looks like a stock 18 spline tranny with a wiped out cluster gear. Okay, I've been street racing and drag strip racing for many years. I've learned the hard way that 2 things have to slip. Either the clutch or the tires with a stick car. Your choice. Over the past 40 years, I have never broke a tranny or rear gear. My car is a street strip car that has dipped into the high tens. Most of the time it is in the very low 11's. This with close to a 2 ton car!!! My combo is very conservative.. 11' Dual friction, 18 spline slick shifted tranny, 4:56 gears with a 29" tall tire. My engine make over 580HP at the wheels. I don't know how you shift. I've never seen you or know you, with that, Granny shifting is very hard on the drive train. Power shifting will lengthen the life of drive line parts. It's pretty hard to power shift a stock tranny above 5000 rpm. Also, what type of gear oil are you using? All of this is my experience and opinion. Take it as you like. I'm just trying to help.