The only way to know is to look at the castings. There are many rumors
and false input around. If you have blue paint lines on them that really means nothing FYI.
Find your castings then you can see what you have!
The 2C5E-6C064-AF & AG
castings were the earliest heads, with four plug threads. Some have the blue paint, some do not.
head was the first update to the driver's side (also with four threads). Some have the blue paint, some do not.
head came out for '04 and had nine plug threads.
head was the final '05 revision and also the FRPP head.