73 340 duster thermoquad spacer ?

No thin paper gasket. Just the thick insulator gasket.

Thremoquad gasket. There is also an open hole version of the Thermoquad gasket, but as you can see, the Thermoquad gasket has a thicker back wall. Using the Queerdrajet gasket on the Thermoquad will result in a vacuum leak around the back of the secondaries. Most stores will try to sell you the wrong gasket, because they want to stock as few parts as possible.
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Queerdrajet Gasket.
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Thanks for the illustration Rob. I figured something was going on. I always thought there was a thin gasket above and below since the original aluminum spacer had a gasket above and below.