Nice module choice, still one of my classic faves.
1e to PF conversions can be a bit tricky out the gate if straight up. giants(and dragons) got huge buffs in the edition shifts. (CR and HD)
You are probably fine with many of the general underlying details. The wizard locks on the doors, the gnolls as the first batch of obstacles. you will need to focus an actual overhaul of the giant army attacking force however. perhaps cut down on the number of thing sin each wave for starters. Not at home so don't have my copy at hand, but that's some advice from memory.
*edit* possible bolster some of the Keep defenses by Bane-ing the ballistae as a field evener.