Why would you want to use aluminum? It will transfer the heat from the intake to the carb. Years ago Direct Connection sold a spacer with a rubber isolator molded in and claimed it was the quickest way to gain a few h.p. on a carbed 2.2. I had one on my Scamp, and I did not dyno. I think it was around 1/2-3/4" tall.
Aluminum also transfers heat faster than ANY material from the intake manifold to the carb. I ran the D.C. rubber spacer for 8 years and it looked like new. You want to keep heat OUT of the carb, not put it in it. In stock/super stock, everyone had as many phenolic spacers as rules allowed to keep heat out of the carb.
The main purpose of a carb spacer is to add plenum volume and make the turn into the manifold less severe. With that in mind, i'd prefer a totally open spacer rather than one that continues the carb bores top to bottom. Alternately you could start at the top with the carb bores and cone them out so that it was wide open at the bottom.
If i was making one, id do that, but that phenolic is probably VERY easy to modify with a die grinder so if it's worth the money to save you the time, it doesnt look like a BAD deal.
Vigo's pretty much got it - I did similar 3yr ago on my dd rampage - IMO - Not worth spending much $ on - Thick gasket will do adequate job for heat tranfer thing & if you raise carb you'll need to shorten throttle cable-mod TC bracket or mod gas pedal attachment - I made an adapter to raise the TC bracket - - - - if done over I'd forgo the carb to adapter thing & instead fab a spacer for between the manifold and carb adapter.
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