Simple method: put a zip bag with kitty litter on top of the intake manifold. Leave enough extra space so that the kitty litter can spread out inside the bag as it compresses. Push the kitty litter inside the bag so that it makes a 3” pile. GENTLY close the hood so that it latches shut. Open the hood, being careful not to disturb the bag, and measure the height of the pile of kitty litter to determine the clearance.
Alternate method: use a 3” wad of modeling clay or Play-Dough on top of the manifold. Put a piece of heavy paper or plastic sheet over the top of the clay. This prevents it from sticking to the underside of the hold. You may want to do the same thing to the top of the intake manifold to keep the clay from sticking to it. GENTLY close the hood so that it latches shut. Open the hood, being careful not to disturb the bag, and measure the height of the pile of clay or Play-Dough to determine the clearance.