You are taking a life threatening
...chance. First, you NEVER use a shackle as your connection to anything that YOU hang on. Tie a bowline and then clip in the shackle as a backup.Second, you NEVER go up on a rope/wire splice.As for the weight issue. Using ascenders elimanates this problem totally. You don't need winches, grinders, or anyone on board. You simply pump your way up with your legs by sitting and standing(very easy).Third, halyard turning blocks handle way more load than anyone can weigh.Fourth, a bosuns chair is a poor(at best) way to go aloft. In a climbing harness, you can get knocked unconscious and not fall. Can't say that of the bosuns chair.