The problem is that that spacer is not primarily a gasket - it is a heat insulator, so needs to be thick enough to give that heat insulation without collapsing and distorting the carb body. In an ideal world, the 2 surfaces will be good enough not to need a gasket - if a gasket is needed, then it should be the thinnest possible that will create a seal - thicker soft gaskets only increase the risk of a leak by pinching the area under the bolts and wedging open the area between them. On that basis, back in '77, I put my Comp engine together on standard paper gaskets with just a smear of grease - the 'Douglas Experts' told me I would never keep the oil in it - that engine has proved ultra-reliable having completed 25 years of vintage trialing and subsequent road use, and is still as oil tight as the day it was built - I rest my case!
Eddie.