Is it possible I didn't get the full save game somehow? How many blocks should it be?
602 blocks. I would recommend downloading the file again from the FTP site. Also, if you have kernel version 5530 or earlier, download the previous version of ltools (ltools_MA_v1.7.5.zip) . Try installing again first with the new 1.8.rc1, and if still doesn't work, try ltools_MA_v1.7.5.zip.
When installing ltools_MA_v1.7.5.zip, you should choose UDE2 install if you are using a North American Xbox (NTSC) and UDE otherwise. The steps are basically the same as UXE.