My experience is the same as Jim's. The switch was made around vin 1,000 but there is some back and forth overlap. '66 production units were all aluminum or all iron. none were half and half . The only cars to have the half and half transmissions were the '67 T/A coupes. This was based on the amount of tailshaft housing failure in race conditions in previous years. NO other production SAI vehicle used that transmission. The Transmission was also used for the '68 T/A season but there were no "customer cars" sold that year. "I" was told the original P.O. was for 100 half and half transmissions. The rest not used in race cars were sold out of the catalog as Jim mentioned until all were gone. I was also told that "warranty" repairs were only authorized to use the cast iron tailshaft housing when a repair was needed. This came from the late Ray Wolfe . One of his titles was Service Manager at High Performance Motors when it was operating. When I used to buy parts from him in the late '60s and 70's he had about ten NOS half and half T-10s for sale.