I think the kit supplied posts might be ok. They have a slight lip rather than fully recess and the bolt doesn't quite go all the way in (about 1mm) because the thread runs out - but even so the new bridge is a few mm lower than the other one - so I think I can afford to raise it a little.
Need to do some more comparison. I think using the provided posts may be a less risky venture for me when filling and redrilling is likely to leave just a slither of dowel and glue.