Sorry, I was simply answering the question of what longer arms you could use, not the legality of doing so in a racing context. I'm in the UK and at our club you can run any chassis setup but limited motors. I would expect in TCS you can only use Tamiya parts. Whether you can mix and match from other Tamiya cars I'm sorry I don't know the answer to that. A wider offset wheel or a wider hex on the rear of a FWD makes no practical difference in my own experience. For a laugh I did once run a set of TL01B (Buggy) rear arms on an M03 with F1 rear wheels for maximum width and it looked very odd but still went round a track much the same.