I think I know the answer but will ask anyway.

Does the free end of the overflow pipe, as fitted to radiator filler neck to cortina radiator need to go into a bottle?

(theory being that when coolant expands, it goes into this bottle and likewise when it cools, the liquid will be sucked back in to the radiator.

Not necessary but a good idea.
It will save on top ups if your system runs a bit hot!

Personally, I run a pressurised system with a float level indicator light on my dash. This is because both my projects are rear engined and I have already knackered a head gasket on my k-series once, because the temp gauge does not show as hot if there is water loss.
At least the water level light will give me an early warning.

[Edited on 10/9/2007 by nitram38]

Can't beat what Dave Andrews has said on this subject (and I do exactly what he says!)

Water link

HTH,
David