You are right, jfs has a 64Gig upper limit ..
To confirm you filesystem is jfs, do
lsfs <filesystem name>
A jfs2 filesystem (which is available from AIX v5 should help )
A note from IBM Website :
The maximum size of a regular file in a JFS file system enabled for large files is slightly less than 64 gigabytes (68589453312). In other file systems that are enabled for large files and in other JFS file system types, all files not listed as regular in the previous table have a maximum file size of 2 gigabytes minus 1 (2147483647). The maximum size of a file in JFS2 is limited by the size of the file system itself.
The architectural limit on the size of a JFS2 file system is 2^52 bytes, or 4 petabytes. In AIX 5.2, the maximum JFS2 file size supported by the 32-bit kernel is 2^40 - 4096 bytes, or just under 1 terabyte. The maximum file size supported by the 64-bit kernel is 2^44 - 4096 bytes, or just less than 16 terabytes.