Mechs use starship rules. Use the hulls given in the book, renamed for whatever mech classes you care to use, but divide prices by 10. Most of the fittings won't be relevant, so decrease each hull's free Power and Mass by 1/3rd or so. Weapons and defenses can be reskinned with different names and are bought as normal, at 1/10th the book price for starship equivalents. From that point on, just use normal starship rules for mech fights. If you prefer to use a traditional BT hex map, then just use it as normal and run the fights with round-by-round combat and initiative as if it were a human-scale fight. Movement rates are X hexes+"Spike Drive" engine ratings for each mech, or double that if they do nothing but move.Spike drive phasing is obviously not a factor in mech fights, but heating is. More advanced engines are better at bleeding heat. A mech can fire as many non-ammo-using weapons per turn as its "spike drive" rating without accruing heat. For each one it fires beyond that, it gains one heat point. At the end of every turn, roll 1d12 and add the mech's spike drive rating. If the roll is not higher than the mech's heat point total, it cannot fire any weapons next round, but the heat total resets to zero. A mech that does not fire any weapons during a round, including ammo-based ones, resets its heat total to zero. Ammo-based weapons do not add heat but cannot be fired during a heat-based shutdown.Phasing is no longer a meaningful weapon quality. Instead, for each point of Phasing, add +1 to the hit roll with the weapon.