Am I right in saying this is the Calibra engine?

Also - If so, was there a difference in the turbo/non turbo pistons? I know one of them comes with forge pistons as standard with valve cutouts

As said, came from the astra mk2 which was the early XE 154 bhp then they changed it to a 147bhp version. which can be found in astra gte (mk2) astra mk3 gsi, calibra, cavalier gsi 2000

you need the pistons for the ZT?

Thats right.
Speaking to Cali16v, the 20xe and 20let pistons are nearly the same until a later model 20xe was made that used cast pistons. The eailer ones had valve cut outs and where forged by Mahle.

I think they used parts from a bin, there are various types used. Astra GSi/Cav GSi and Calibra J reg and earlier and the GTE's used Cosworth cast heads and Mahle forged pistons. But they actually used some of that stuff again in some of the later engines. Some of the Cavalier SRi's used 16v heads and some used 8v heads.
And then some of the 2litre standard Cavalier LS cars had an XE.
The turbos had different Mahle pistons, but the only way to get these is to get them from Vauxhall for £££££. No real answer though, the early engines had 'COSCAST' stamped on the side of the head. These are bombproof and have the pistons you are looking for.