So it isn't really like the Armored Core RP requires actual stats. It's more weight and build specialization. From the old RP:
The Armored Cores are divided into three weight categories: light, medium, and heavy. The lightest are the fastest and most agile, but also fragile. They specialize in lighter weaponry, but can equip heavier cannons and missiles at the cost of their speed and maneuverability. Heavy ACs have massive physical power with a much higher load capacity for weapons and ammo, but are slower. The legs types of an AC also determine its movement and combat type. There are three types of legs: biped, quadruped, and tank. Biped and quadruped legs come in the three weight categories, but biped legs are also divided by standard or reverse-joint structure. The reverse-joint structure has less load capacity, but is suited for jumping and aerial combat. Quadruped legs are the opposite, geared solely for ground superiority and maneuverability. Tank "legs" are different, coming in two types, tread and hover. The tread tanks have the highest load capacity and can even store full-sized weapons in specialized compartments, but are slow and difficult to maneuver. The hover tanks have very low load capacity, but combine the ground and aerial maneuverability of the quadruped and reverse-joint leg types.
Weapons setup:
Arms: hand-held/wrist-mounted
Back: mounted cannons
Shoulders: mounted; usually flares, decoy missiles, extra propulsion, extra missiles
Hangars (stored in leg-panels): small backup weapons
Back-mounted weapons are best reserved for the things with higher recoil because you have more stability (and are referred to as "cannons" - laser cannons/sniper cannons/gattling cannon). That said, heavier ACs can equip parts with higher recoil on either arm due to their greater weight-bearing capacity. The arm spots are best kept for weapons that require more dexterity and aiming in fast-paced combat (blades, machine guns, assault/rifles, etc).