Thanks Jim for the article. I hope to get delivery of my 69 in a week, but know the rears are missing the shakers and also likely the fronts as well, as the car has a Speedtech subframe with an LS swap done a few years back and probably were removed back then. I'm still not sure why anyone would remove them purposefully, unless they are an obstruction. Like relocating a battery to the trunk, the shakers aren't taking space otherwise. I also cam across this article for gen one Camaro verts which was help explaining the canisters. I guess, I'll need to drive the car a bit to determine whether I'll need to get them replaced. Hopefully not, as they seem to go for a premium in the secondary market and I guess no one makes an aftermarket version at the moment.

http://www.chevy-camaro.com/faq/chevy-camaro-convertible-cocktail-shakers.shtm#:~:text=A.,lack%20of%20the%20roof%20structure