Which header tank

[SeriesLandy]

Hi guys, I'm now at the stage when I need to buy a header tank for my car but I have no clue which one to buy (rover, golf, corsa ect)
I want to mount by the nose cone and I've seen that some people are using one from a corsa. I realise the cap pressure would be wrong (pinto) so can I just stick the cap off the sierra tank onto it, or would it be the wrong thread?

Hopefully someone can help as I'm more confused than when I started looking.
Cheers