So I started talking with a friend of mine, and this started to happen.
El Basic Fluff:
With advancements in Quad battle armor allowing the onboard computer to figure out foot placement for the pilot, More exotic mech configurations became feasible.
A mech with 6 legs, rule chunks in no particular order...
A: 6 legged mechs are only 1 level high.
B: May go prone or stand without movement cost.
C; Reduces the cost and limits of level changes by 1. aka Going up or down 3 levels cost 2 MP. 1 level changes are free, like Wiges.
D: When determining the direction an attack comes from, use the Vehicle table. aka more side hits.
E: Each leg is limited to the structure and armor of an arm for a given mech's size.
F: Hit table, the important bit, Left and right sides remain the same. Leg and Arm hit locations are resolved on a special hit table, similar to a tripod mechs leg locations. On a 1-2 the front leg is hit. on a 3-4 the middle leg, and a 5-6 the Rear leg. If an attack comes in from the front apply a -1 modifier, if the rear a +1 modifier. (aka, an attack from the front will hit the front leg 3/6 of the time, middle leg 2/6 and rear 1/6 of the time.)
G: Damage transfers into the side torso.
H: -2 Piloting roll like quads.
I: must lose 2 legs to loose that bonus, like a quad losing 1 leg.
J: Critically damaged legs can be jettisoned to avoid movement penalties from critical actuator damage.
K: Takes half damage from falling due to failed PSR checks. Takes full damage if it somehow skids off a cliff or something.
More optional rules...
L: Leg crit tables are 12 crits, but actuators take up twice as many slots. I think this one is going to be dropped entirely.
M: If the mech is prone at a higher level then whatever is shooting at it, Hits on the actual leg location on the hit table are eaten as though the mech had partial cover. Arm locations still activate the secondary hit location table.
N: I'm not planning on changing the construction rules. Standard structure weight. Maybe I could see a 10% increase to structure weight, same as a tripod. But thats still only 1 ton increase in weight at worst. No big deal.
O: Front legs guns shoot forward, Middle can choose front or rear (Must be designated as rear firing.) rear legs shoot rear only.
Game Balance is mostly compared to a quad. extra mobility, extra leg armor, though legs are more fragile individually. But it looses the ability to fully exploit partial cover and other benefits of being 2 levels tall that a quad has. Its also going to be prone to having its side torso's blown away due to the changed incoming attack direction.