73 340 duster thermoquad spacer ?

Spacer, no. But the correct gasket is already over 1/4 inch thick...
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So this one is the correct gasket
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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So the first picture the gasket is the correct one and the one on the bottom is not