House Rules for a Post-Apocalyptic Earth Ravaged by Dimensional Breaches

I get my main inspiration from the Siege Engine by Troll Lord Games.

Right now I'm still using the Breaches Attributes, but I use the Siege Engine Attribute Mods & Primes. Humans still get 3. Everything else gets 2. I'm conscidering adding another, due to the extra number of Attributes OR switching to Siege's Attributes.

Primes, however give a +5 Bonus.

Basically you still select Skills per Breaches, but your Rank is simply equal to your Level (however any +X% or divided by 5 is applied). Weapon Skills prevent you from having a -4 Non-Proficiency penalty & adds a damage bonus equal to Level/5.
Hand to Hand Training: Basic gives you a BAB of Level/2 (equal to a Mage).
Hand to Hand: Expert gives you a BAB equal to Level x 3/4 (equal to a Cleric).
Hand to Hand Martial arts gives you a BAB equal to Level (equal to Fighter) +1D6 bonus on any Melee damage.
Hand to Hand: Assassin gives you a BAB equal to Level + 1D6 bonus on any Ranged damage.

Any Saving Throws are handled by Attributes.

I use the D20 System Difficulty Class system for Skills checks & Saving Throws.

And the D20 System Armor Class system for Combat checks.