All classes are legal for play except the Gunslinger and all 9th level casters. Bolt Ace Gunslingers can be homebrewed to use with the atlatl. (See below). Specific deities either don't exist, or are unknown, so any class that requires worship will just worship a concept.
All characters start at 5th level, have 20 point buy, and two traits. The stone age rules for gear are in place. There are no crossbows or swords, in their place are atlatls and terbutjes. Check with me on any equipment you use and we can adjust or reflavor it if necessary.
Every time you level up just use the average die roll for your HD rounded up to calculate HP. 1d6 is 4, 1d8 is 5, and so on.