Early cars, like this ’68 Camaro, used a two-bolt (3/8 x 16 thread x 1.25-inch) transmission mounting pad. Later issue (prox. 1982-up) used a single bolt (10mm x 1.5 thread x 1.25 inch) for the pad-to-crossmember attachment. If the mount shows any sign of wear, replace it with a new OE assembly or stronger one from the aftermarket.
Now unhook the speedometer cable, vacuum lines, and the linkage and move them out of the way. Put another jack under the engine oil pan to keep rearward tilt at a minimum once the transmission support has been removed.
Position the four locating tabs on the transmission jack beneath the pan so that the weight of the case is distributed evenly. Raise the jack slightly to take the weight off the crossmember. Remove the crossmember.
Remove the shift cable and shift arm from the transmission. Early (prox. 1981 and earlier) ones are secured with a 3/8-inch nut. Late units use a metric (10mm x 1.5 thread) fastener.