You can define on or more calenders public on mavericks or the web and enter the url in leopard to get a read access. The shared calender is duplicated and accessable by everyone who knows the url, but will not be shown at the google search results.
The Google calender works like iCloud for the private link to the calender. You get a read access without entering the login data. For write access (to other users) the calender must be public and will visible at the google search results.
Maybe you will find some solutions for a two-way-sync at the web. Dropbox is no option, because it is only a web space without the functions from a caldav server.