If I understand your idea right, I think the split bridle may be a mistake. If mast starts to move to one side a split bridle will just move with it. You might maintain the same tension of both shrouds, but that does not mean they will hold the same distance.
On my Dana I added a hinging joint on the upper shrouds, and the same height as the mast pivot point. These pivot points were each separately secured forward with low stretch line. The secured shrouds prevented side to side movement (or restricted it at least). Then line over gin pole (with also required restraining lines to the sides) with block and tackle and could raise and lower mast on our own Your Mariah mast is going to be heavier of course, but same approach should work. Sorry, this is very difficult to describe in words.
One point: If the boat is in the water
when you raise the mast, be aware that side loads can get very high when raising mast. As mast is being raised if mast swings a bit to one side or the other, the boat will as a result roll a bit to that side, which then increases the swing of the mast even further to the side, which of course rolls boat even further... Do not underestimate the potential for things to go wrong.