Hi Paul,
Welcome to Ope!
You can use any 242 pistons in a 42 jug, but not the other way.
The only piston you dont order is a Meteor 242, for some odd reason Meteor choosed to lower the crown and also use longer shirt.
If you can afford it, a Tecomec 242 top end kit is a good choice, a buddy of me have used tecomec 242 a half year now, it's a strong runner, but the kit itself is quite heavy.