I think a spacer, is a spacer....just a glorified packer to increase volume of plenum , so long as it doesn't leak they will be OK
Thats cool then, so its possibly high flow cats, then spacer, or would you spend an extra £100 and get a kinetix planum?
gains are the same, no hard evidence that full plenums give more gains thatn spacers.
With 2 gaskets (as it's supposed to be anyway) it's not gonna leak...
also try motordyne, they do nice packages. I'm waiting for Josh off 350z-tech to sort his own, $165 shipped