Generally 1EP=1WP, based on Grey Star, etc.
I sort of prefer EP - after all what's a Kai's Willpower and when do they get it? 10-19 at Rank 10/Master I'd say.
Anyway, here's my house rules for the Gamebooks.
Basically Vakeros 'Battle' Magic is based on CS and Brotherhood Wizard Spells on EP - e.g. Lightning Hand "CS" is your current EP, very powerful to an uninjured character! Remeber Banedon's words when he meets Lone Wolf at Raumas. It seems my ideas were on the right track seeing what Mongoose printed in Heroes.
Attack Spell:[Round Zero Offensive Action]
Invisible Fist/Power Word [MM] Treat as Non-Edged Thrown Weapon attack. -0EP to cast.
Lightning Hand [KA] Treat as an Edged Thrown Weapon attack but compare your current EP (not including Armour) instead of CS for Combat Ratio. -3EP to cast.
Net [KA] Treat as Non-Edged Thrown Weapon Subdue Stun attack but compare your current EP (not including Armour) instead of CS for Combat Ratio. No effect on Doors, Fire-Emitting and Non-Corporeal foes. -0EP to cast.
Hold Enemy [MM GT] Make a Disarm test without weapon/armour modifiers, if successful enemy may only parry for the same number of round as the <Random Number> picked. -0EP to cast.
Defensive Spell:[Round Zero Passive Action]
Elementalism Air - Buffeting Winds -1EP Damage received each round -2EP.
Elementalism Earth - Kazim Skin, +2CS. 2EP to cast.
Elementalism Fire - Firebolt, as Kai Battle Crystal. -2EP to cast.
Elementalism Water - Ice Blade, creates a fragile normal Weapon from thin air, destroyed if your enemy inflicts more damage than you. +1EP damage to Fire-emitting enemies. -2EP to cast.
Elementalism - Summon Sprite. An Elemental Ally who will not attack but will retaliate if you are attacked; in Melee every time an enemy wounds you they take -1EP damage, includes foes immune to normal weapons only if you are able to harm them. -1EP to cast.
Invisible Shield [KA]/Shield [MM] Creates a Shield +2CS (suitable for GM). -2EP to cast.
Mend [KA] +5EP or repairs one non magical item, must be cast in water. -0EP to cast.
Vigour [KA] +3CS for one combat, may not be used if EP below 10. -3EP to cast.
Energy Grasp [MM SL] +1EP damage inflicted when fighting Unarmed.
Strength [KA SK] +2CS +2EP when fighting Unarmed, (+3CS +3EP Wizard, +5CS +5EP Sorcerer) -0EP to cast.
Flameshaft [MM KGG] Arrow does +1EP damage (+50% Sorcerer). -0EP to cast.
Penetrate [MM SL] +1CS (+2CS Sorcerer) to one Arrow, may be cast with Flameshaft. -0EP to cast.
More (including explanations) here
http://www.mongoosepublishing.com/phpBB2/viewtopic.php?t=42027&start=0&postdays=0&postorder=asc&highlight=
Banedon in Magnamund Companion Spells:
Lightning Hand -3EP
Invisible Shield -2EP
Vigour +3CS, -3EP (Cannot cast if EP less than 10)
Counterspell -2EP
Levitation -2EP
Mind Charm, Net, Sense Evil, Mend & Silence free - Mend requires fresh running water.