Volvo introduced the aluminum case in the M46 as a running change in the 1985 model year. In turbo 700 series Volvo introduced the P type overdrive as a running change in the 1986 model year. While the J type is a fine OD, the P type is stronger. J type ODs will not interchange with P type ODs because the transmission output shaft (which drives the OD) is different.

An M46 from a 240 works in a 740, whether turbo or not. You will need to change the output flange at the rear of the OD, the shift linkage, and the ball stud for the throwout bearing. The ball stud for turbo 700 series is near the slave cylinder, while on the NA cars it is on the far side of the input shaft.