In the good old days of V8's and carbs--spacers were placed under the carb. This in effect created a longer intake runner length --which force air to run faster in the the chamber b/c of length it has to travel in short.

This type of theory may also work well with a TB at increasing plenum effective runner length. Don't knock until the dyno shows it to be false.

Not that its worth 80bucks, traditional dometic V8 spacers were often made from High density plastic and cost around 20bucks???