I am in the process of building one of those, too, and GWilliams is probably right; the torsion bars are probably just primer red (brown?), although I painted mine Gunmetal (wartime pictures I've seen of torsion bars being installed on a Tiger show them to be a dark grey/black; it's hard to tell in black & white photos, but I assume they're covered in some sort of a protective coating, either grease or maybe a German version of cosmoline?).
I also painted my radiators steel because a.) the pictures I've seen of tank radiators (specifically, the radiator shrouds on Tiger 131 at Bovington) show them being left unpainted, and b.) it gives a bit of a contrast to the overall OD finish of the Ersatz M10.
However, I got hung up on the tracks; I've never done link-and-length track before, so it's taking me a while to get over the intimidation factor (plus, I'm still learning how to attach them effectively). With any luck, I might actually finish it this year!
1/48th Monogram A-37 Dragonfly: 95% (so close!); 1/35th Academy UH-60L: 90%; 1/35th Dragon "Ersatz" M10: 75%; 1/35th DML E-100 Super Heavy Tank: 100%; 1/48 YF-12A, 95%; 1/48 U-2R: 90%; 1/48 B-58 Hustler: 50%; 1/32 F-117, 50%; 1/48 Rafale M: 50%; 1/48 F-105D: 75%; 1/48 SOS A-1H Skyraider: 50%; 1/48th Hobby Boss Su-27: 50%; 1/16th Revell Lamborghini Countach: 75%; 1/12th Otaki Lamborghini Countach: 25%; Tamiya 1/35th M3 Bradley Cavalry Fighting Vehicle: 25%