My experience is with 240s. Someone else, ( probably Art ), can weigh in on the difference in your 740. You will have to ( go to a wrecking yard, or get one from a member, an electric locker for the driver door. Connect it with a coat hangar to the lock.
Then, all you do is tie in to the locking relays behind the dash. If you don't want to disassemble the door, you could still have the other three doors unlock remotely, which is way better than no remote lock at all.
Later, you could do the driver door, which is not too difficult, but it is time consuming.