Transbrake stageright
I have a kit that I bought from Brian Hofer that I didn't use. I bought it thinking I was going to install it in my old tranny but I ended up just buying a complete tranny with all the bells including a stage right transbrake from Brian.
I still have the kit including the custom detent plate for your shifter so you don't accidently slide the shifter it into 1st (transbrake) while doing 50 down the road.
You will of course need to install it or get a tranmission guy to install it. It has detailed instructions and pictures in the instructions.
D.