I think it would be possible to create a career-style progressions system for ACKS, not unlike Warhammer 1e/2e. Each career would equate to 1 level in 1 class.

Here’s some examples:

FIGHTER

Gain 1d8 hit points

10% chance attract followers if a fortress built/owned

20% chance 1 general proficiency*

20% chance battlefield prowess

33% chance 1 fighter class proficiency*

66% chance +1 attack throws with axes in any armor and fighting style*

66% chance +1 attack throws with bows/crossbows in any armor and fighting style*

66% chance +1 attack throws with flails/hammers/maces in any armor and fighting style*

66% chance +1 attack throws with swords/daggers in any armor and fighting style*

66% chance +1 attack throws with spears/pole arms in any armor and fighting style*

66% chance +1 attack throws with bolas/darts/nets/slings/saps/staffs in any armor and fighting style*

66% chance +1 saving throws*

Career Cost to Enter: 2,000xp ^ 2x(# of prior careers -1)

MAGE

Gain 1d4 hit points

Gain 1 level of arcane spellcasting ability

Gain 1 level of magic research ability

10% chance to attract apprentices if a sanctum has been built/owned

15% chance 1 class proficiency*

20% chance 1 general proficiency*

33% chance +1 attack throws wielding quarterstaffs, clubs, daggers, darts in no armor either one-handed or two-handed*

33% chance +1 saving throws*

Career Cost to Enter: 2,500xp x 2^(# of prior careers -1)

THIEF

Gain 1d4 hit points

Gain 1 level of thief abilities

10% chance to read and cast magic scrolls

10% chance to attract apprentices if a hideout has been built

20% chance 1 general proficiency*

25% chance to read languages

25% chance 1 thief class proficiency*

50% chance +1 attack throws wielding one-handed weapons, either one-handed or duel wielded, in leather or lighter*

50% chance +1 attack throws wielding missile weapons, in leather or lighter*

50% chance +1 saving throws*

Career Cost to Enter: 1,250xp x 2^(# of prior careers -1)

*Automatic if this is your first career.

EXAMPLE: Duran selects Fighter as his 1st career. He gains 1d8 hit points, 1 general proficiency, 1 fighter proficiency, +1 to saving throws, and +1 to attack throws in a variety of weapons. The cost to enter is 0. He chooses Fighting Style (Two Weapon Fighting) and Riding as his proficiencies.

After accumulating some XP, he selects Thief as his 2nd career. It costs 1,250xp to enter. He gains 1d4 hit points. He gains 1 level of thief abilities, so he is effectively a 1st level thief on the table. He rolls for other bonuses. A roll of 80 means no read magic ability; a roll of 64 means no read languages; a roll of 54 means no general proficiency; a roll of 66 means no thief proficiency; a roll of 39 grants +1 attack throws with one-handed weapons in leather single or dual wielded; a roll of 44 grants +1 with missile weapons in leather or lighter; a roll of 65 grants no save bonus.

Duran would now fight with…

Attack throw 10+ using an axe in plate armor (+1 from fighter)

Attack throw 9+ using a sword in leather armor (+1 from fighter, +1 from thief)

Attack throw 7+ using 2 swords in leather armor (+1 from fighter, +1 from thief, +1 from 2 weapons, +1 from proficiency)

Etc.