Installing headers into a small block V8 engine?

It can be done, and may already have a sort of header installed. New headers would require reprogamming the computer or a chip to compensate for the the decrease in exhaust pressure. I doubt if it would gain you enough mileage to pay for the headers, etc. A good tune up, keeping your tires properly inflated, clean air filter, easy on the gas and brake will get you more mileage.

The purpose of headers are to make an engine breathe better, but without an large air intake you wont get the maximum horsepower. Id pass on the headers and purchase a good chip to upgrade the ecm for more power.

You'll also need a driveshaft from a V8 Monza and make sure the transmission has a short tail on it so you won't have to take it in to have the driveshaft shortened, Great advice from chevyraceman-383. Make sure to put a frame and proper rearend in it, I got my frame from Alston Chassis works, You'll have a ball in it, I have a 383 stroker in my 77 Monza Mirage. I had to get my motor mounts custom made because I couldn't find them in any parts stores by me, (My motor mounts were bad because the oil pan was resting on the K frame.)