Yay for monsters stolen from century-old pulp fiction stories!
Girallons have some very nice melee traits. Magical beast type, large size, high strength, a good speed, and no less than five natural attacks.
However, their eventual LA comes down to a single question: can girallons wield weapons? I'm going to say they can. Not only are they said to be similar to gorillas, which have opposable thumbs, their picture also implies tool use. Sure, they've got claws, but plenty of monsters with claws can use weapons (kobolds and lizardfolk come to mind).
So what does this mean? Well, not only can a girallon wield 'normal' weapons, they can also choose to use a modified one usable in four hands (per Savage Species) or go nuts with multiple-weapon fighting (I'd love to see a girallon using Girallon Windmill Flesh Rip). That said, I'd recommend to keep at least two arms free for that sweet rend damage, at least until enemy defenses start requiring special weapons to overcome.
All things considered, I think +1 (or maaaaybe +0) LA fits best. Feedback is appreciated, admirable and also awesome.