Updates on Installing on Unlocked Bootloader with Custom recovery
I downloaded the OTA above for my phone model (Karbonn Sparkle V) . I had unlocked bootloader for my previous CM 12.1 ROM. So the procedure is simple, I rebooted to recovery (PhilZ Touch) and then formatted data, system and cache. I then proceeded to install the zip file which automatically installed the boot and system.
Now I'm running a fresh 6.0 Marshmallow build while still retaining my unlocked bootloader. All things are running fine. Now I'm going to setup my SD card as an internal memory, before which I need to reformat it as I had partitioned it to run Link2SD.
All the best lads!
Edit 1: Use Custom Recovery option, uncheck the recovery checkbox. Do not the install from zip option directly, I lost my custom recovery that way. Re-installing recovery now.
Edit 2: I advise doing it the plain old, lock your bootloader, flash boring stock rom way or the phone will cause issue with the internal memory.