You can buy the bottom part one month; buy the top part in six months; then buy a good harness separately, if you plan to go sky diving, from 12,000 feet.
it is more expensive to mix if you dont keep say like a openshot top you already had.most likely you would be better off to sell your old summit and take money and buy a OPENSHOT TOP WITH TITAN BOTTOM.
i sat in openshot with titan bottom and it was GREAT .much better than before but i like lots of room on floor.......