Are convertible parts such as the rain gutter, stainless steel trim, cocktail shakers, etc. compatible between camaros and firebirds of the same year?

For the most part, yes the differences are between years as are the Camaros. Such as bright verses dulled trim, padded verses chrome pillar moldings. Most parts fit all three years and both models but I’m not sure of the 69’s front cocktail shakers.

As for the cocktail shakers, 67-68 are the same, 69 front and rear are different.