Yeah that is why I think this is just the 4.0.3 with some minor changes. AOSP doesn't have a branch for it yet in Google's code which generally releases as the OTA is announced or slightly before it.
This build is going to be 4.0.4 I have the signed leak of IMM26 that is signed with the proper codes and can be installed with Odin without bypassing the signature checks. The build prop of those files also has the signing key hashes. The release structure of numbers from my understanding was 4.0.1 and 4.0.2 were reserved for the Galaxy Nexus. 4.0.3 was reserved for the Nexus S non 4G and the early tablets such as the XOOM WiFi. 4.0.4 is for the Nexus S 4G and other devices such as the XOOM LTE. 4.0.5 would be a new release train that is capable of building for all devices and have all changes merged together. Whether this is true remains to be seen. But building 4.0.3 does have the 4G known to work but it did not include the bootloader that is mentioned on Google's own page and even fastboot complains when you build 4.0.3 from source for the NS4G. You have to build 4.0.3 as an OTA package or it will not install on the NS4G because it missing the new bootloader which is not made available until an OTA. Until I have word from somewhere and a link that points me back to the link on Google's server I will be leaving my ROM alone and using the 4.0.4 proprietaries. Even using Google's own number schemes we know IML74K is 4.0.3 so by reason IMM26 is 4.0.4 but 26 may not be the actual release since the GNex has a leak of IMM30B which is also 4.0.4 so the IMM26 leak may actually be what was going to be released but got pulled for some reason and now the build has changed to IMM30B. Which makes more sense Google rarely releases a build without a letter after the number. IMM26 is probably an internal testing build. I would expect the release to be a higher variant of either IMM30 something that we have not seen yet.