The SR Ranger ended up starting at 9th level as a 1st level cleric with 1 spell. It then alternated between gaining access to Magic-User and Cleric spells, and using a combined spell slot matrix to contain both - at 8th and 9th, 1 first level spell, 10th and 11th, 2/1, and at 12th and 13th, the matrix is 3/2/1 (3 1st, 2 2nd, 1 3rd). As comparison, a 5th level OD&D Magic User would cast at 4/2/1, and a 5th level Cleric at 2/2.
The 1E ranger gave the ranger a more regular pair of progressions starting at 8th in Druid and 9th as a Wizard, and ended up at Druid 2/2/2, and Wizard 2/2. A 3rd level Druid in 1E clocks in at 3/2/1, and a 3rd level Magic User is 2/1 (4th is 3/2).
We're going to be a touch more limited than that. ACKS provides us a framework of Arcane and Divine build points, starting at 1/3 level for Mages, and 1/2 level for Clerics. We'll do 1/4 level on each side (one could argue that we'd do 1/6 for Mage, since it's half of 1/3, but the Arcane point progression is 'broken' anyway, since it goes 1/3 to 1/2 to 2/3 to 1, so 1/4 is one-half of 1/2 which works better.)
Half Value Spellcasting
For the price of a single build point, a class may split its casting ability between Divine and Arcane. This single point grants the class the ability to cast as a Mage and Cleric of 1/4 its level, rounded up [ceiling()] for Divine and rounded down [floor()] for Arcane.
The class may Turn Undead as a Cleric of 1/4 its level.
The class may Turn Undead as a Cleric of 1/4 its level.
A class may delay availability of its spellcasting. The class may alternate gaining spellcasting levels (first Divine, then Arcane) starting at Level 8 with Divine casting, as in the table below.
This is intended to even out and spread out the spells available to the Arcane and Divine sides, as in the Strategic Review Ranger. The fact that ACKS uses the B/X concept of Cleric not receiving spells until 2nd level causes us to grant one non-casting level of Cleric before we start the alternation.
Whether or not the class can cast Arcane spells in armor is a matter left to GM preference.
The class's Divine repertoire is based on 3 Divine spells per level.
Half Value Spellcasting costs 425 experience points. A class may not take more than 1 point in Half Value Spellcasting.
ALTERNATIVE 1: A class may choose only one of Arcane or Divine to advance as a 1/4 level caster. If so, allow the class 1.5 proficiency slots to be filled by the class designer as normal. The class may trade in Turn Undead (if the Divine half value is kept) for another half a proficiency point.
ALTERNATIVE 2: A class may delay spellcasting in the regular manner, by gaining a level of each class starting at 11th as in the table below.
ALTERNATIVE 3: The GM may opt to match the Divine progression to the Arcane by bumping the effective Divine level by 1 at levels 4, 8 and 12, as in the table below.
