With 61-64 strike length cells forward you could still have VLA and TLAM leaving the 64 tactical length cells aft full of ESSM and SM-2, a very formidable load out.The RAN didn’t have the people to crew the Kidds, FFGs and the Anzac class. Something has to give and FFGs 1-4 is the obvious short straw. End of life of these ships was 2008-12 and even Darwin would have been 22 years old if it decommissioned to crew Anzac 8. FFGs 5, 6 would last to 2020 and could always be kept in service with SM1 decommissioned like the USN does its FFGs. They could serve as northern border patrol frigates in the meantime leaving the Kidds and Anzacs the warier roles. 14 DDGs and FFHs is the best option for the RAN in this timeframe.
The issue is height not the surface area footprint. Mk 41 strike length are about 1/3 higher than Mk 26. You might be able to fit in tactical length VLS to the aft section if you really need more than 61 missiles. It may fire rockets but it isn’t rocket science replacing Mk 26 with Mk 41 would be relatively straight forward especially as the RAN could accept the tactical length launchers not needing to shoot TLAM or VLA.
Not getting the Kidds was dumb and probably caused many of the crewing issues experienced from the late 90s.