I have used a bottom end from a Focus RS.
The compression ratio whould have been 6.3:1 if I bolted my head straight on because the Focus RS forged pistons have a large dish in them.
So a large head skim is required (or new pistons) I also fitted longer rods.

I am now up and running but have not been on a rolling road yet!

I had a 1.9 CVH which was running 27psi and 320BHP but this Zetec build feel a lot quicker!(lights the tyres up at 25psi in 4th gear).