Thank you Boxtaboy and JFP for the confirmation - it was just down to dumb luck that I attached it as I did, not noticing the spacing difference until after the fact.
But I do now admit that I find it quite odd that this part does not come with any sort of a "This Side Up" marking, as it is obviously super easy to flip it around the wrong way.
Gelbster, I know what you mean about those U-pipes! But that will be work for tomorrow, as I am working in an unheated garage and I am done for the evening.
Since this issue has come up, here's a couple of work-in-progress pictures of one of my pair of gutted secondary cats. I cut the end of the canister off with a band saw, removed the heavy (7 pounds each!) metal honeycomb core, and then rewelded the end cap back on it.
End result should be a nice stealth look (disclaimer: for off-road use only of course).
Thanks - DM