Machined aluminum port adapter. When switching from a big port head to a small port head, but maintaining the original intake manifold, this is the adapter you need.
Early model 4AG's were a big port design with a TVIS (flapper plate) between the intake manifold and the head. The flapper plate had 8 ports and would restrict airflow at low RPM's to increase the air velocity into the head. At high RPM's the flappers would all open and allow more flow into the head.
The later model 4AG motors came in a small port layout to increase velocity into the head throughout the entire RPM range. They eliminated the TVIS plate entirely.
The problem when putting a small port motor into your big port car, is that your big port intake manifold will not match the small port head.
This adapter fixes that. It is the exact same thickness as the TVIS plate and allows you to bolt the big port manifold directly to the small port head.