I made a cut out and enlarged on both ships. IMHO all are the normal square canisters for C-802.
SM1 is out of production. The only remaining version of the Standard missile 1 in service is the RIM-66E (SM-1MR Block VI). While no longer in service with the USN, the RIM-66E is still in service with many navies globally and is expected to remain in service until 2020. These current non-US users either have domestic/used OHPs [e.g. Poland, Egypt, Taiwan, Spain] or have Mk13 equipped domestic ships [e.g. France, Italy]). So, in any case, you'ld be looking at RIM-66C/D Standard SM-2MR. Which is unlikely to be had by Pakistan in the current situation
I would agree with Mk41 + an IIRH or ARH missile (like CAMM). If relations with US preclude this, a Sylver A43 or K-VLS could be a good alternative. Possible a Chinese VLS with quad packed SD-10. Primarily because this improves firepower without the need for much more than installation of a new 3D search rader to replace the old US 2D radar.
The supersonic Standard missiles, being semi-active radar homing, can also be used against surface targets. This gave the Mk13 with 32 SM1 and 8 Harpoon great sustained anti-surface fire power. However, I doubt a 40 Harpoon load out for the Mk13 would be the most usefull (there's a fairly large change of the ships being put out of action before they can use up all these AShM in action). Plus, you'ld be stuck with 1 Perry that doesn't have. For a moment I thought, possibly, the Mk13 could fire ASROC, which could improve the ASW potential of the ships. However, the Mk 13 GMLS is not able to fire this weapon, as the launcher rail is too short (
http://www.eugeneleeslover.com/VIDEOS/Asroc_Weapon_System.html). But in all cases, this is US weaponry. And I don't see, if US refuses to deliver Standard missile of whatever kind, why they would deliver such numbers of Harpoon or other missiles.
Another option would be to remove the Mk13 arm and used that space for e.g. a 24-round FL-3000N. If you build a small deck house right over the Mk13 base, it would be feasible. With a bit of luck, Harpoons could fit as on PNS Alamgir. If Harpoon can then not be mounted forward, it could be put atop the superstructure, just like on Taiwanese ships.
The Taiwanese ships are interesting due to having 2 additional 40mm cannon and AShM atop the superstructure.
The Australian modernized Adelaide class is interesting due to SM2 and Mk41/ESSM
The Turkish G-class are interesting due to modenization of the CMS and use of Smart-S Mk2 (the Mk41/ESSM aside, since this first done by Australia)
Some US ships sport an additional weapons platform forward, over the Mk13 base
PNS Alamgir is interesting due to forward mounted Harpoons