Beefed up My six, need more power to the Rear

Okay I've taken my 225 Slant 6, Bored .60, Head milled 0.100, With Clifford Performance Torq-er cam, and Twin Weber 38's intake, and headers.

Still same 727 trany, and stock rear-end, I don't think I'm getting the power that it's supposed to have though to the Tires/Road.

Thinking of getting the Transmission Rebuild and Shift-kit installed, and need a better 3rd Member...Any Suggestions?