No, Harbah is shorter in length. A safe estimate would be 450km (same as Babur-III).
No, not yet. Babur-II (now IB) and Harbah are indigenous(-ish), and will take time to mature as anti-ship weapons. Till then, Zarb/C-602 serve as stop-gap.
Zarb itself can't be termed as upgraded C-602 (with respect to avionics/range). What I meant was that the version of C-602 which Pakistan imported (and later modified to Zarb) was already an upgrade to the white-painted C-602 often pictured. This can be confirmed by matching the Pakistani Zarb to the Chinese YJ-68's training round, they are exactly the same in appearance.
I know exactly how things in Pakistan work
I suggest that you read PN's publication again, to understand why Pakistan changed the designation of C-602 to Zarb. It has nothing to do with ToT, range extension or an upgrade (so to say). They didn't even change the paint scheme of the training round.