Yes they are substantial changes. My post above was written at the same time yours went up so I didn't see it.
There are a lot of issues with a pre 86' boat, I touched on some of them, but they all boil down to a boat that won't self right (realistically) and is prone to turtling (almost unrecoverable without outside help). It also means you can't snag cheap sails from racers or use published tuning guides.
The boats are very different though they look the same.