About to take on a transmission swap on my 1966 Tempest custom. It has the orginal 326 and the ST300 trans. I found a heck of a deal on a BOP TH350 for $50. As far as I know they are compatible with spline count/length.. only thing is the trans I bought was missing the speedo gear/housing. Got the housing but the speedo gear is a tough one. Apparently there are multiple options and I'm not sure which one to go with. Can anyone here point me in the right direction? Please help!