True -- I haven't seen flow testing for those manifolds either. I've kinda, somewhat tested my own stock manifold before (100% stock) and after porting (sawed open, hogged out, and welded back up). I did the testing using individual EGT monitors on each header runner. While I'm the first to point out that the EGT method leaves a good bit to be desired in terms of accuracy, there didn't appear to be any significant amount of flow imbalance up to ~28 PSI. That's contrary to internet wisdom that says the stock manifold has a flow imbalance, but IMO that internet wisdom may be bogus, just as I believe lots of other bits of internet wisdom to be.
On a somewhat related note, I have a avid drag-racing acquaintance here in Florida who about 3 years ago was running a T-88 on a stock long block with 272 cams. He switched to a big Supra shop's prototype "pipe style" intake manifold that used the stock lower runners welded to the pipe, and with some sort of thottle body on it of course (I don't recall what TB he used but I think it was the stocker...). With the switch to the pipe style manifold the car slowed down in both ET and Trap Speed, and broke up on the top end. Troubleshooting revealed nothing wrong with the fuel supply or ignition. He switched back to the stock manifold and the car ran normally again. I say this to say that I am suspecting that the race teams that run the pipe style manifolds do more than just weld runners to any old pipe and slap a throttle body on it.
