Indeed, the result if we can't change some of the cooling system would be VERY samey, as there's only so much room to fiddle around with and you'd have to make them energy heavy because otherwise they are grossly inefficient.
So with this one, I know you don't like changing what we can do with the structure of the Mech but with the Warhawk, to make it interesting and useful, we -need- some of the heatsinks removed. Its got 13 installed in the engine and a total of 20, it's fully up to you how much we're allowed to go to but I'd suggest a minimum of 13 (so only the 3 extra built into the engine) or 16. Even removing 4 would free up 8 badly needed chunks of space. Reducing it to 15 would be better, as its then only one in each side torso and gives us 10 tons of space. 13 tons would be ideal but lore wise that might be a bit of a push, although they are pod mounted and should be easily removed.
This could also be applied to the Executioner, another mech that was lamed by having a huge number of heatsinks installed. With the Gargoyle it makes sense (kind of) you can lore wise say they are all safely put in that huge engine and IIRC they are. But with the Warhawk and Executioner, there's a lot more outside the engine which should be easily removable.
And I just checked the Executioner comes with 16 heatsinks, 15 of which are mounted in the engine. So one could be removed. Sure its not much but still its something.