I recently acquired a 1977 BW Super T10 out of either a Camaro or Firebird. My question is about the speedometer gearing. I have a 66 El Camino with a factory 3.36 rear end gear in it. Can the speedo drive gears be changed without breaking into the transmission ie. externally, or will it require an internal and external gear change like an automatic? I'm not sure what ratios the mid 70s F cars had from the factory so I'm not sure how much of a change is going to be required to calibrate my old school mechanical speedo. Any help will be appreciated. Thanks!