Jonny, as it's a conversion, you shouldn't expect too much of a grilling on Navigation aspects, and the exam will be shorter.
However, I'd say that's the only real way it differs (or should differ!) from the YM Sail exam - on mine, the examiner used every opportunity to refresh on
- Lights & Shapes
- Seamanship Knowledge
- Safety Briefings and Crew Management
Specific areas which we expected to be tested on (and mostly were) that ensure you are a good power candidate too, include:
- Diesel Engines
- Radar (As a Collision Avoidance tool, and a navigational tool)
- Fuel Consumption/Ranges
That said - the close quarters stuff is a bit more straightforward, and tends to be a little more relaxed regarding doubling up lines (i.e. Bow lines used as a spring also etc) and such. We didn't anchor at all. The examiner also requested that we didn't use the bow thruster unless we really had to - we didn't!
It's a short conversion exam, and is pretty straightforward as long as you go in with all your skills and knowledge still tuned - if you're rusty, it may catch you out.