Would help if you actually posted the manufacturer of the header. They are not all the same.

 

Well because he didn't do the work in selecting and installing the parts himself (had garage do it) AND they're already heat wrapped, I am not 100% sure on the brand. Although they did charge him $800 back when he first bought them and he recalls them starting with the letter P. I know, I shook my head too. My best guess is that they're Perrin.

But I guess I should be more clear on my question, it's more broad than "does this specific header fit my specific car". My question is, what prevents headers from fitting certain WRXs and STIs. Is it oil pan related?

 

The flat oil pan in the EJ205 is the cause for the discrepancy. Easy fix: replace the oil pan with the 2.5L variant.

Perrin header will necessitate an oil pan swap

 

Wouldn't a new oil pan mean I'd need a new oil pick up and all related stuff too?

 

It wouldn't be a bad idea to replace the flat bottom oil pan regardless. Spirited driving can cause the OEM setup on the 2L to suck air because oil will slosh from one side of the pan to the other.

 

Interesting I'm guessing that would be a good time to buy the Killer B oil pickup right away for peace of mind.

Alright thanks for the info guys