HG's still around...I think. Mostly trick show Traxxas parts if I remember right.
A lot's improved since back when and I don't think you'll see your diff nut problem anymore. That diff in your B4 should be about the same as what came with your GT (so AE claims), so even if you have some heartstoppingly powerful motor in back, the nut should hold
I've been running Associated electric trucks indoor for about 7 years now and I've only seen this issue come up once (and I think it was on a Losi