Fabrik8

They might have a flow bench. A flow bench will tell you where the restriction is though, because you can flow test the rest of the manifold with and without the throttle body. Ultimately it's still an iterative process of making a change and seeing if it is a positive change or a negative change. You can never go wrong with something like Extrude Hone though; just smoothing out the runner wall is a good gain, even if you don't actually increase the runner diameter noticeably.

You can do some of the same things with a MAF that you can with a flow bench, but the results aren't going to be as accurate and you won't be able to get as much useful info. You'll also need something to datalog the MAF obviously.