Planet of the Apes Light

I got the urge to do a simple (two or three page) classic Planet of the Apes style hack for Swords & Wizardry Light. I have Apes Victorious and it's fantastic, but I want something even more rules light. There's not much work to be done for this though right?

The thief and fighter classes work fine for the setting. I'd need to make quick ape subrace and devolved human races and stat some primitive firearms (which I've done for Six-Shooters & Wagons). I think the game needs more classes than two though. I would also definitely stat out some supporting characters and such.

What else should I add to this mini project?