Of course, boat repairs are never as simple as you expect. As I went to remove the first screw that holds the control block to the jib lead the head broke off. There was not enough of the screw body exposed to put pliers on it so I needed to drill out the screw body. The only way to do that without potentially damaging the jib lead was to remove the jib lead from the track and drill out the screw body from the back. This got most of it and a hole punch got out the rest, threads intact! The remaining screws came out without a problem. Compared to the new blocks, you can see how much of the sheave was missing.
A little blue locktite on the screws and the new control blocks were installed. I took the opportunity to lube the ball bearings in the jib leads cars while I was at it. Everything all back together and running smoothly.