I've ran both, honestly could not feel a seat of the pants difference.
I've run a nwor tri-y (basically looks to be a thorley) and a generic long tube 4 into 1 for several years each. The generic had a paper thing flange that leaked like a sieve but had great torque from around 500 rpm up when coupled with my 2.5" tubing - no cat. I lost the bottom end grunt when I changed to 2.25", but every thread in every forum says 2.5 is too big so I must be wrong... The nwor is built much, much better, but I've never been able to tune to it decently, though it will rev to the moon. I partially blame my cam.
I now have the nwor, lce and downey headers and like certain aspects of each. I feel each are well built and are likely about the same performance-wise, but am going to run the lce to see what difference making only that change will make, if any, though I am going to swap from the crap-tastic weber carb to a 22r carb. Hopefully the carb change will not affect anything, which it shouldn't being they're within 1 cfm of each other.
End thread jack
