how far do i go

[Bonzo]

Hi Andy

I am far from an expert in this field but here are my thoughts for what they are worth.

Being as your donor was a darn fine runner, I would be inclined to leave the CVH as standard till you have had your IVA.

To fit the carbs onto the CVH you'll be needing to make an inlet manifold to suit. I would imagine that the jets may need replacing or fine tuning for the engine to run smooth & meet emission targets.
Do you really want the hours & hours of work fine tuning the CVH engine just for temporary use.

When you change to the Zetec engine, you'll need to start from scratch all over again
The carbs set up for the 1.8 CVH are not likely to run so well on a 2 litre Zetec. A fair bit of power difference between the 2.

I think the carbs you mention will be OK for either engine but probably best suited to the Zetec unit.