From a recent posting on this blog:
Got dick? has a reading with a mass interpretation (“body-part conversion” of C to M, as in Kim is looking for dick this weekend). ["sex-part conversion" in this Language Log posting on zero relationships]
Jillette is trying to grapple with this C>M conversion, accurately getting the multiple-cock understanding of the first alternative, but struggling to characterize the cock-as-undifferentiated-substance connotation of the second, which he says treats cock as a verb.
Fogarty and Jillette agree that the second is the better porn title. So do I, though I note that big cock works somewhat better as an object (of verbs like crave or want, or of prepositions in verb complements, as in look/hunt for) than as a subject (Big Cocks on Parade is an attested porn film title, though Big Cock on Parade would also be possible).
(A further note: both big cock porn, with the base noun cock, and big cocks porn, with a clearly plural modifier noun, are attested. The first is the default compound construction, but there is a fair literature on cases with the second construction (some discussion here).)