I'm pretty sure it won't effect anyone on this thread, but it is something I should mention for others reading it. (And similar)
We all love bargains! Heaven knows I've done my fair share of sourcing equivalent components and buying second hand for the Westfield over the years, and will no doubt do in the future too.
But one of those things to keep in mind when building AND having to pass IVA, is that Westfield make a kit and supply parts capable of passing the test. Amongst other reasons, it one, why sometimes their parts are dearer then slightly similar parts elsewhere, (or even identical parts, supplied elsewhere).
Don't underestimate this "commitment" the factory gives when you buy a part from them!
A quick story! I had one of the first batch of the stainless re packable trackday silencers, they launched eight or so years ago. The one that looks identical to the stainless one in the link!
it failed SVA (as it was then) for the radius on the outlet pipe being too small. It shouldn't of, it was a production mistake at the manufacturers, as Westfield had spec'd it to be SVA friendly. The factory offered to swap it with a new one from the next batch, or to get me though a retest, make up an adaptor. I went for the later option, and they rushed me a slot in adaptor with an extra generous rolled lip on it, in double quick time, and at their cost. I duly passed.
Not all equivalent parts, supplied direct, come with such assurances. So don't forget to check, it's something that might affect you.