Your cylinder heads have A.I.R. ports drilled into them:
Also, your exhaust manifolds have ports cast into them as well"
The exhaust manifolds have a passageway and flange at rear of manifold which the aspirator valve (or air pump) lines attach to.
The picture above, someone cut that line about two inches (5 cm) out, flattened, then bent over and flattened again to crimp off the tube - which is something I see a lot of (in non-emissions states or cities). DO NOT do this if you live in an emissions state or city! In my state, Oklahoma, they don't care what you do.
Other options are:
Find or make a metal plate to bolt to rear of exhaust manifold. The factory plates are very hard to find.
Here is a picture of a new engine with one installed:
A person can also make a plate as well. The hard part is finding a gasket - but it wouldn't take much to make a gasket using header gasket sheets.
If you plan on using headers then the only other way is to tap the holes on cylinder heads and insert metal plugs in the holes. This method is the best way - but there is limited space with engine in car to perform this operation.
The last option is to find mid/late '70's/early '80's exhaust manifolds that have no provision for A.I.R. holes:
See earlier manifold to see the differences.
BudW