helicoil in heads

68A,
the TA heads are the 'J' 915 castings and are the same as any of the 915 castings. The only difference was in the machining of the heads for the TA (six-pac) engines. As Fishy68 said, the push rod 'tubes' have been machined outboard for offset rockers to allow for additional porting to widen the port more than is possible with the std. 915 castings. In the as cast form they flow the same as all the other 915's, because they are the same. But they can be made much better. Given to you...WOW what a friend. You should do something for his birthday.
Terry.