3 You’ll need an adapter plate to mount the two-barrel-type TBI unit to the four-barrel manifold. This is required whether you’re working with the stock Q-jet–type spread-bore design or an aftermarket intake with a Holley-style square-bore design. Note the counter-sunk fasteners at the rear of the adapter plate. They’re necessary to provide adequate clearance of the TBI unit. This plate is easy to make, but aftermarket plates are available for $50-$75.