Tuff motors for drums, never thought on that. way better looking than perms.
but custom parts are.... cheating.
try to use many weapons in same place

(pic from B.Bros)
like this.
damage is increased alot.
remove rear axle mounts, and use their weight for more weapons.
Square and round extenders have the same hitpoints(100) and a iron spike, if well placed can hurt some weak spots.(i did it on one of my crappy designs. Piston included, 2 servos for maximum mobility, but no more weapons(Rule of 7). later version replaced with axe head, but still WAAAAAAAAAAAAAAY uneffective. especially on SCv3 bots.