It's nearly a good design for a turbo manifold. Look at furburgers, and you'll notice that the runners are straight for a couple of inches before the collector. The straightness helps minimise the stress on the collector when the whole thing's red hot. on the regal one, there's no straightness, and to be fair to regal, there's no real need, as it won't be stressed anything like as much in a NA car. I'd also be surprised if thinwall stainless steel can take the heat and stress over a reasonable length of time.
As far as lengths go, getting them all the same will mean a massive torque spike, if they are different, then the torque peak'll be lower, but spread over a bigger area. this is the case for N/A. turbo stuff will be similar, except that you want the lengths as short as possible as the turbo wants pulses to make it spin, not a constant airstream, which is contrary to what you'd expect.
If you want to experiment with size and clearence, you can always make a mock up out of mild steel, and get it made up in stainless.
If you are going down this route, then at least get the advice of a respected (ie not regal) turbo tuner and/or manifold designer.