I was curious about this, so I looked it up. From what I can tell, it's not clear that 'awful' and 'offal' have any etymological relation; they have different roots, with the first being related to "that which inspires fear" and the second being related to "to fall off" (i.e. that which 'falls off' the butcher's block) (https://www.etymonline.com/word/awful) (https://www.etymonline.com/word/offal). 'Awful' used to have much weighter connotations of something which induced dread, whereas 'offal' was apparently more about refuse - not something dreadful, just something unwanted in the way waste is unwanted.Casual Shinji said:Guts' name also stems from him being seen as worthless muck by his adopted father. Another word for guts is offal, which I believe in the olden days was used as an insult, and I assume where the word 'awful' comes from.
That said, I do think you are right that Guts' name is meant to relate to 'offal' and its root meaning by its evoking imagery of spilled innards and everything about them which is grotesque, unclean, and calling to be disposed of.