1965 Plymouth Barracuda Transmission or Gear Vendor?

I have a 1965 Plymouth Barracuda that I have recently restored. I put a 408 stroker in it with a 727 transmission and a 373 positive rear end. I'm looking to either change my transmission or add a gear vendor to obtain overdrive. Which would be the best option - a 4 speed automatic transmission or a gear vendor? If recommending an automatic transmission which one would you recommend?

Thanks in advance for your suggestions!