I would not modify the shrouds, as then your sheeting angles for the jib will not be able to be hauled in tightly enough when sailing close hauled to the wind. Your ability to perform under sail should always be the most important consideration. Also the hull would have to be modified & reinforced considerably where the new chain plate attachments are to be installed. You would be surprised how thin the fiberglass hull layup really is where the hull attached to the deck on a C 27. Its about a quarter of an inch thick at the upper most point of the hull, & thickens as it tapers downwards towards the water line, as all boats do. I remember seeing a Pearson 30 that was hulled through from hitting a dock piling in a bad storm, & it was also only about a 1/4 inch thick at the topsides of the hull. Its surprising that more sailboats don't oil can implode in the hull under heavy sailing. Its really only the combination of the main bulkhead & rigging that keep them together, & the geometry of the shrouds is essential for proper performance & load distribution.