it is not, I wish I could have gotten the best of both worlds, but you gotta pick one or the other so I decided to do the 23 spline with the 2:47 road race setup, the main case and tailhousing is aluminum, I already have a 11" big block aluminum bellhousing from american powertrain, I mostly do autox, would like to do some roadracing in her someday, I'm not drag racing so I didn't need the 18 spline setup (that and the price tag starts over $3000) whereas this setup was around the $2000 mark which is a easier pill to swallow, especially with our terrible dollar exchange rate