Further on the Yaksha, I'm thinking 9 HD is too much for them, no matter that it fits with the "Fights like OD&D Stone Giants" bit.
They're supposedly weaker than Rakshasa, so shouldn't they have less Hit Dice? I'm thinking 6 HD, like a Jann. If we do that I'd like to increase the Con to 19, so they have around the 50 hp of the original. Besides, if they're dwarf-like creatures they ought to be tough!
We can have them advance to Large size, which'll give them the same physical stats as Stone Giants. That seems a good way of covering both ends!
Armor Class is 2 worse than a Rakshasa, so I'd give them a NA 2 less than a Rakshasa's +9. I think Damage Reduction X/magic is appropriate, but I could be persuaded otherwise. They should probably have Spell Resistance too, just not as much as Rakshasas!
Weapon or slam attacks I guess. Let's say 2 slams like a Genie. Greatclub would fit the "fights as a Stone Giant" bit, but I'm tempted to give them a martial weapon. Perhaps a Greatax?
I'm also thinking they should be able to take on the form of human(oids) and animals, since I vaguely recall tales of them shapechanging into men or beasts to delude folk.
Finally, I favour "Always chaotic" for alignment, as that covers the full range from helpful (CG), indifferent (CN) and maneating (CE) nature-spirits.
Putting it together I get something like:
Yaksha
Size/Type: Medium Outsider (Native)
Hit Dice: 6d8+24 (51 hp)
Initiative: +3
Speed: 40 ft. (8 squares)
Armor Class: 20 (+3 Dex, +7 natural), touch 13, flat-footed 17
Base Attack/Grapple: +6/+10
Attack: Weapon +10 melee (xdx+4 or xdx+6) or slam +10 melee (1d4+4) or rock +10 ranged (1d10+6)
Full Attack: Weapon +10 melee (xdx+4 or xdx+6) or 2 slams +10 melee (1d4+4) or rock +10 ranged (1d10+6)
Space/Reach: 5 ft./5 ft.
Special Attacks: Rock throwing, spell-like abilities
Special Qualities: Alternate form, [damage reduction 10/magic?], darkvision 60 ft., low-light vision, rock catching, [spell resistance CR+13?]
Saves: Fort +9, Ref +8, Will +6
Abilities: Str 19, Dex 17, Con 19, Int 13, Wis 13, Cha 15
Skills: 9 at 9 ranks
Feats: 3
Environment: Warm forests and hills ?
Organization: Solitary or family (X-X) or clan (X-X) ?
Challenge Rating: 6?
Treasure: Standard coins; double goods; standard items ?
Alignment: Always chaotic
Advancement: 7-12 HD (Medium); 13-18 HD (Large)
Level Adjustment: +7
Alternate Form (Su): A yaksha can assume any animal or humanoid form of its own size or smaller as a standard action three times per day. The yaksha can remain in its animal or humanoid form until it chooses to assume a new one or return to its natural form.
Rock Throwing (Ex): Yakshas are accomplished rock throwers and receive a +1 racial bonus on attack rolls when throwing rocks. A yaksha of at least Medium size can hurl rocks weighing 20 pounds each (Tiny objects) up to five range increments, with a range increment of 180 feet. It uses both hands when throwing a rock. A Large yaksha can hurl rocks of 40 to 50 pounds each (Small objects).
Rock Catching (Ex): A yaksha can catch Small or Medium rocks and projectiles of similar shape, a Large yaksha can also catch Large rocks.
Once per round, a yaksha that would normally be hit by a rock can make a Reflex save to catch it as a free action. The DC is 15 for a Small rock, 20 for a Medium one, and 25 for a Large one. (If the projectile provides a magical bonus on attack rolls, the DC increases by that amount.) The yaksha must be ready for and aware of the attack in order to make a rock catching attempt. Yaksha have a +4 racial bonus on Reflex saves when attempting to catch a thrown rock.
Spell-Like Abilities (Sp):—invisibility (self only); 1/day—create food and water, create wine (as create water, but wine instead), major creation (created vegetable matter is permanent), persistent image (DC 15), wind walk. Once per day, a yaksha can assume gaseous form (as the spell) for up to 1 hour. Caster level 18th. The save DCs are Charisma-based.