Kyle,

Your concept is right, but the SU manifolds used on Volvos are way too short to have an affect on tuning the torque curve. Spacers won't make any difference.

With the full heatshield used with HS6s, I've never found any need to insulate the carbs from the manifold, beyond whatever the normal paper gasket offers. GRM found they made a difference on their 122 project car, but that one had heat shields meant for HiF carbs, which don't protect the HS6's side-mounted fuel bowls.

You may be able to widen the torque curve with long air horns (I don't know this for a fact -- never had horns on SUs myself, and don't know how they work with the variable venturi). Remember it's the total length of the intake that matters, not just the manifold length. Then you're up against inventing some sort of air cleaner/air box sorta thingy, and maybe cutting a big hunk out of the inner fender to make it fit...

So, I'd say forget all that, go with the standard setup, and save your pennies for some future head work. You'll like the carbs just as they come.

--Phil