[CobraBob]

Are you asking for the measurements between the four base plate holes? It sounds so. If so, I will check the measurements quickly from my T-56 shifter gasket. Be right back.
Bob Arthure
Stang Shifter Gaskets

 

[CobraBob]

This may or may not be what you're looking for, but here are the measurement for the T-56 shifter base bolt holes (center to center).
3 7/16"
2 15/16"