The size of the heads on the starter bolts was originally 19mm. At some point in the late 80s, it was changed to 18mm. Check before you buy a socket, if you are only getting the one. You want the kind where the U joint is part of the socket, not two separate pieces.

You will also need a long extension----18", or even 24". You can use several shorter ones together but this doesn't work as well, due to the play in the joints, which adds up, when you put two or three of them together.

On a 740, you can often get the top bolt with a box end wrench (15 degree angled, like the box end of most combination wrenches) from the top. There may not be enough room on a 240 to do this.