Is it really necessary? The BoL magic system can more than handle demon summoning as written whereas Crimson Blades, being a form of retro game, needed specific demon summoning rules.

What about adapting the Demon material from Legends of Steel?

All I can think is to assign Difficulty and AP costs based on CB spell levels.

As for spells done the Vancian way, the character could know Mind+[equivalent magic-user career] worth of spell levels. and the equivalent magic-user career level would limit the spell levels you can use. If you want the players to know more, you can multiply the number into itself, so the result would make for an exponential build-up of spells as you gain career levels.

With summoning, you can establish what kind of spirit you can get at each magnitude. A first magnitude summoning could summon a lesser demon/elemental/undead. A greater demon/elemental/undead for second magnitude And a demon/elemental/undead lord with third magnitude.

Optional, you could do it like in Carcosa*, where the Sorcerer needs to setup a summoning with a series of complimented spells to contact, summon, restrain, torment and bind a spirit to the summoner's will, with each step requiring its own spell-casting. (A little over-kill, but it really makes summoning drown-out, flavorful and suspenseful in the nail-bitting way!)

*A dark, twisted CoC-type fantasy setting by Geoffrey McKinney.