They *should* fit,it's too early for my brain to function. There may be an issue clearing the K5/6 oil pan,but cant remember cause I just woke up :hammer

 

Yes, K1-K6 headers are interchangeable.

 

Another question then. I'm looking at some yoshimura titanium headers. What the chance of the connecting pipe being in the same place as the stock so I can fit my m4 to it. The opening is 50mm.

 

That is different between the generations, but from what I understand it can be made to work.

 

Is the standard outlet 50mm on a k5 thou?

 

A popular mod is 5 - 6 headers on previos models; the 5 - 6 have bigger tubes, better flow, so your going wrong direktion.

 

They're yoshi ti headers so should be an improvement on the standard k5 ones(hopefully) I have doubts now?

 

See this. It sounds like K3/K4 will fit K5/K6. But the reverse is iffy.