Purchased and converted to Aperture last month
How did you convert to Aperture? Are you using your iPhoto Library as your Aperture library?
and a block of my iPhoto projects are missing
That is ambigious (due to Apple's confusing terminology) - do you mean iPhoto events are not showing in Aperture as Aperture projects? Or are you asking about iPhoto projects (books, calendars, cards) that are missing?
If you opened your iPhoto library as Aperture library, you can still open it in iPhoto. Have you checked in iPhoto, if the library is still containing all the missing items? If they are still in the library, write down some filenames, event names, keywords, so that you can use these to search in Aperture for the missing library items. You can search in Aperture using the smart search field below the browser.
If the missing items are no longer in the converted library, can it be that you imported these events into a different iPhoto library? Have you searched for additional iPhoto libraries?
Does your converted library contain a "recovered" project?