Check with our site TRANNY sponsors for sources. Gauge manufacturers also sell the electronis/mechanical adapters. I use the (011) or aftermarket transmission and not the OEM replacement tranny for this and other conversion/install reasons.
Sewe this link for some other points
http://drivetrain.com/gmt56inst.html I have also found a 15 degree clocking issue as it interfaces with the scattershield or bellhousing.