Those raised bosses are there in case you want to drill and tap for temp sensors or such. The only 351W intake I've found with a water passage that goes from head-to-head across the back of the intake is the Chinese Typhoon (also marketed as the Summit house brand), although there may be others...
I bought the Summit 'Stage 2' Performer RPM-type clone because I wanted a place for both the factory electric temp gauge and a mechanical temp gauge as well... I've since taken that POS off there (terrible core shift that does not match head port locations) and replaced it with a Torker II