If they really were trying to emulate droop present on a real PR they would probably have made a point of telling people, at the very least to be able to gain some points on striving for hard-core accuracy. However, giving that they already idealized parts of the Thomson and stock I doubt they set out to make a PR with a crooked barrel. (But then this is just me taking informed guesses.)
I am generally not one to complain about the yay or nay of hard-core accuracy either way but in this case I really would prefer a straight barrel even if the originals were all crooked. (Would a gun smith really build live-fire rifles with a crooked barrel even if they were only going to fire blanks?) The quirks and wonkiness of certain props adds to their charm, like the asymmetry of a Trooper bucket, but a drooping barrel on a state-of-the-bad-ass-art hardware just looks wrong.
However, that interior photo of how the SPAS cage was assembled seems to clearly indicate that they were not purposefully assembled in a crooked manner. It just looks like they were tying to get them done so quickly that they didn't wait for the glue to dry or something.
