I would regard these as a "nice to have" on a mildly modded car, not a necessity

 

As mentioned drop Carl Davey a mail, I'm sure I read an article where he was working on this and seemed to really know his stuff.

Also if ur inlet manifold is comin off he does some spacers to prevent heat soak from heads to inlet.

Carls Scooby Site ver.2

 

if you fit the spacers remember you will also need extra 'normal' gaskets
top and bottom of spacers