I did this over the winter when the 331 was being built so I had idle time.
BBK welded the primaries to the header flanges on the inside which I am assuming was to make room for the header bolts. Some pictures of what I started with and what I ended up with:
Here is the side by side comparison, I had one header completely ported and the other is as is from
BBK
Here is the one ported by itself
Its kind hard to see what I am talking about in the first two pictures so I zoomed in and just concentrated the pictures on one port.
Here is the unported picture
Here is the ported picture
You can see that there was a pretty good obstruction in each one. I then moved to the collector area which is what most call a fire cone due to the type of connection or at least that is what I remember it being called. Measured both and they were right at 2-1/8" on ID. Searched around on the net and mostly the Corral and found that this is nothing new and that JBA is about the only one with a true or close to 2.5" ID. I took a black Sharpie and ran a 1/8" thick line around the opening of the collector where the X-Pipe slides on and proceeded to open them up. I was a bit leery of 2.5" as I wanted to make good and sure these things sealed back up right. Nothing worse than an exhaust leak....tick, tick, tick...annoying as all hell. Here are some pictures of what it looked like before and after.
Stock
BBK collector opening (you can see the black Sharpie outline):
After I marked the lip with a Sharpie and used a 4" grinder to knock the lip off of it. You can see the wide, flat edge that is shiny:
And the finished product measuring 2-3/8" ID. Not that it would gain me 15 hp or anything but I just could not leave it alone:
Here they are side by side so you can really see the difference: