I used 1" steel rod threaded on both ends on an elm about that size couple of years ago. Had a 4' drill bit on a gas powered drill to make hole. Bought the rod from metal supply, rented the drill from tool rental place and had a plumber thread up the steel rods. I think split will heal over after rods put in also, it looks like it has split and healed a few times from the amount of bark along split. Couple of rods should help hold it shut. Some cables up higher would not hurt either. Can't see whole tree but looks like it would be shame to lose.