Greg, Vaux XE NA pistons are fine for ZVH conversion, but too high a CR for Zetec 16vs For a 16v use Calibra ones.

Id personally not bother using then at the moment, purely as they are becomming an arse to find decent sets...also id not use them much above 300bhp.

PS. Ive seen people quoted for rings at £200 a set I pay about £40 incase you get stuck....same for machining, if you get stuck, jus shout.