Tom, I've made this conversion a few times and drawn up a few more. Most of the time you have to install a bow sprit to get the CE moved far enough forward, so you don't have a lee helm
situation, which is dangerous. On a boat with a long keel
, the conversion is much less demanding, assuming the CE balances over the CLP is a reasonable location (lead) for the specific rig.
Most often the chain plates cause the biggest issues as the Bermudian rig and the gaff typically need them in different locations, so making the Bermudian caps fit the gaff can be a challenge.
In the end, all things are possible, but frankly, it's not a difficult task for a designer
, though the well meaning shade tree boat nut, will likely have balance issues, without professional help. It doesn't cost much if you have a well known design.
As for the back stays, yep, it'll have to go, but the gaff rig is a low stress rig and running backs are not as much a problem as you might think, once you get used to them. Unexpected jibes can be an issue, but the wise sailor will have a preventer, if the point of sail or conditions suggest it's needed.