Thanks to Gaieus and Dave R for answering my question and the follow up re components verses groups, I have tried your suggestions and they are as you say. However for now until I get more experience with SU I am going to continue with groups, a bit more work as you say but I can edit each part quickly and when I come to dimension each part hopefully it will be simpler.
By the way Gaieus. Waistcoats are not so pointless when you live in England.