converting to running backstay
There are three ways that running backstays are usually added and they all involve adding a strong mounting point. The normal backstay is left in place in all most cases. The easiest and sturdiest mounting is to beef up the transom and add chainplates on the transom off of the centerline. The chain plates need to be sturdy enough that they do not flex and fatique under load. The comparably flat angle of this installation reduces the load on the stays. Runners installed at this location are less vulnerable to being hit by the boom during a jibe. Retractors that pull the runners up out of the way are also easier in this location. For all of those reasons this is the prefered set up on race boats. The down side is that they are less easily removed for storage and can be in the way of bimini''s.
The second set up is to add chain plates to the hull on either side. These are mounted on the topsides. The topsides need to be beefed up to distribute the loads. This is a simple, sturdy and straight forward set-up. Runners in this set up must be played on each tack and are harder to get to and more in the way than on the transom.
A popular cruising set up has pad eyes in the deck. This is the hardest to build structurally as this usually requires adding structural knees or tie rods to bring these upward loads from the deck to the hull structure. They are easier to get to than rail mounted backstays but are most in the way and have the greatest chance of being hit by the boom.
By the way adding a jibstay, is by no means an easy task. Properly done, the deck needs to be reinforced and a tie rod or bulkhead or both added to take the large upwards loads of a storm sail. The jibstay should be removable because sailing with a jibstay is a real pain in the butt on most sloops. (Real cutters have a differently proportioned foretriangle which helps with this a little.)