no gains except for the guy who's selling them, he will gain $100 in his bank account for a $2 part.
Adding a spacer to a carb'd engine can increase the air velocity down a very short manifold throat and into the manifold and heads. With the length of your air inlet and considering your injectors spray directly in the intake ports the only real gain you can ever hope for will involve increasing the amount of air/fuel into your engine, then getting that burnt fuel/air out.
Adding length, or even swirling the air as some companies claim will do zero. Save your money for something that will help. A chip, a cold air kit, headers, etc. Even these will only slightly increase power as the Cologne V6 is limited by the heads and how much they'll flow. Forced induction is really the only way to make big power without major re-configuration of the heads, cams and exhaust.