Slant six spark plugs and numbers
Your engine obviously has the 1975 model year and newer head on it. It still may be the 1973 block with a swapped head or maybe the whole engine was swapped out. See post number 6 and 10.
The guys on slantsix.org have been doing this a long time and have settled on the NGK #3459 (ZFR5N) plug as being the best for most people. (The extended tip gets the spark deeper into the combustion chamber) I generally followed the recommendations of @slantsixdan for parts and they've worked well for me. I recently bought another set of NGKs from Rockauto but mine are still good after 10,000 miles. Check with Autozone, Advance or O'Reillys but you may have to order them.
The vehicle VIN had to be stamped into the engine block starting in 1968. Look for a machined pad below the #6 spark plug and see if it matches your car.
EDIT: These are the plugs I used in my early drool tube head. Not for use in later head.
Your engine obviously has the 1975 model year and newer head on it. It still may be the 1973 block with a swapped head or maybe the whole engine was swapped out. See post number 6 and 10.
The guys on slantsix.org have been doing this a long time and have settled on the NGK #3459 (ZFR5N) plug as being the best for most people. (The extended tip gets the spark deeper into the combustion chamber) I generally followed the recommendations of @slantsixdan for parts and they've worked well for me. I recently bought another set of NGKs from Rockauto but mine are still good after 10,000 miles. Check with Autozone, Advance or O'Reillys but you may have to order them.
The vehicle VIN had to be stamped into the engine block starting in 1968. Look for a machined pad below the #6 spark plug and see if it matches your car.
EDIT: These are the plugs I used in my early drool tube head. Not for use in later head.