Just to clarify - your intentions with the Crossfire are to leave the catalytic converters in place, but move the downstream O2's out of direct exhaust flow by spacing them out 1.5"-2"?

That being the case, I can see where you're going with it - you're trying to open up the exhaust piping as much as possible by remove extra blockages (O2's) within the pipe, correct? I don't think that would cause an enormous improvement on the Crossfire. The O2's themselves don't create all that much of a restriction. Yeah, they stick into the pipe, but the hot end of the sensor is drilled out to allow the exhaust to flow freely through it.

On the WRX you were able to see a nice gain because (at least, I think) you did this mod in conjunction with removing the 3 catalytic converters. Removing the cats is what would have caused such a nice gain with moving the O2's having little effect.

If I'm completely off base with what you're planning, let me know. The above thoughts are just based off what I think your goals are with your mod.

I do know, however, that adding a 90* bend in the exhaust in which you can mount the O2 sensors would be a bad idea. You'd end up causing more turbulence and could throw off the whole rhythm of the exhaust system.