Raveners are basically Hydralisks
So yes the weapons are in their chest plate instead of on the arms; for this reason you can get away a bit more so with them in not having to have them perfect for
WYSIWYG. The original editions did carry guns, then the second edition of them in metal simply had arms with no alternative weapon choices (though genestealer claws were good for rending claws on them). Plastic edition they've got proper chest weapons.