Thank you for the very fast reply BigChimp ...!
I'm not sure how to use FPC 2.7.1 ... I did look for it a few times now (i.e. VLC support seems to need 2.7.1 as well).
I guess I'll just be patient until 2.7.1 becomes mainstream.
I did notice however that "zipdetails" (MaOS X command line) does give the proper size. Not exactly perfect, but it will have to do for now until Zip64 is supported under Lazarus.
For unzipping I'll use "funzip" (also MacOS X command line).