I hope I have achieved my original intention which was to identify pitfalls and offer some support for those with original RPCs or Virtual Acorn on a PC. Knowing what to try and what not to try may help. I am quite happy to try to support anybody attempting PDF conversion for the first time. It is worth getting one or both of the programs working.
Since writing the above I am on a different project - writing a book on antiques with several photos (sprite files) on each page. For this I have swung in favour of GS8 over RiScript for the following reason:
RiScript can't handle publisher documents with sprites larger than about 1.5Mb in size. It converts a certain amount of the sprite file and just stops. GS8 has no trouble and gets there in the end.
There are a few other little niggles that I will write to Drobe about unless folks want me to post them here.