My thought is that the speedo gear takes very, very little torque to drive the speedo, so almost anything to hold it in place will probably work.
John
CEREAL KILLER the location of the gear in the picture is where it needs to be and you can see where it currently is located but the lager smooth part of the shaft. You are also correct they have different out put shaft for different tails. Mine is a Ford shaft and I am using a S10 tail for better shifter location. Sure I could replace the output shaft but that is more than my abilities will allow.
www.jalopyjournal.com/forum/showthread.php?p=2994438
I've seen another thread somewhere, but for the life of me, I can't rememeber where it was.
http://www.inliners.org/Jack/T5tech.html