The video below too wayyy to long to figure out how to get working correctly!
Now for the details:
I have an OBDII bluetooth scanner that I bought on ebay - it was like 10 bucks shipped from China (of course).
I have an Android phone running ICS - there is an app thought I bought on the Play store called Torque - it was 5 bucks.
I actually data logged the entire run - and finally got the data to import into video software correctly.
I logged the RPM, Speedo, G force, and various other gauges that you want. The app saves it as a .CSV file that you can open up in Excel.
I used the pc application Race Render 2 - and it will compile the go pro video - and sync up with the Excel .CSV file - and allow you to throw gauges onto your video.
After 2 days of screwing around with the video - I finally got it working!
Now for the same video above w/ gauges!