Type R Plumbing

[MadDogMoggy]

I had a test fit of the engine to sort out bracketry, and I'm now looking at the plumbing. It seems straight forward enough:

two large diameter pipes from radiator connect to two large diameter pipes on engine.

Two small diameter pipes from heater unit connect to two smaller diameter pipes on engine.

However, I also have a header tank (Rover) with a small pipe and a very small pipe - how does this plumb in?

Also does it matter which way round the two heater and two radiator pipes connect to the engine?

Thanks for any help!
Tim