everyone - need keel solution
The smart assed answer is to track down the leaks, repair from the exterior and take the boat to Florida to use or sell!!
Reading between the lines, you haul the boat in the winter and expose the now wet ballast to freeze/thaw cycles further exacerbating the problem.
The elegant fix is a modified #6. The lead has a unit weight nearing 700#/CF. It won''t take near the volume or total weight of lead to replace the 90#/CF sand (You can concentrate the higher weight lead lower in the keel structure yielding an equivalent righting moment). With a little effort and a little engineering calculation you can design the lead ballast to provide the equivalent righting moment. Fix the leaks, install the lead, secure with epoxy. In capping the lead in the bilge area, you should end up with a deeper bilge because of the lead/sand conversion. Be sure this area is dewatered during dry storage.
Now, all this is a lot of work. But any of your fixes (save the scuttling option) will be a lot of labor with a relatively small material cost. I can see the overlay work related to trunk repairs will be difficult due to access for surface preparation and laminating. Not mentioned in all this is the new set of skills required to cast lead, epoxy overlaying and epoxy grouting.
The "let it drain" option seems flawed because you don''t know if the current breach is at the low point of the ballast cavity. It will still be subject to freeze/thaw.
How much do you want to have a "bonding" experience with your Irwin?