Good luck with the test Mike I took mine in my Sabre last year. Would guess you really have to watch the observation in a Spartan with visibility being a bit more limited - I really need to put a cushion in mine as I struggle, esp with the smokes on.
If you havent got them already get some of Marcus Glenns big convex mirrors they are a big help!
Although I found the test quite straightforward it certainly wasnt in the 'drive it once round the field' category that some would have you believe. For a start the examiner insisted it was on public road (in a housing estate), and it involved a number of laps in either direction, and parking up in various places, then a few highway code questions. I passed but main thing i was picked up on was position on road esp at junctions so watch out for that, its very easy to go too far right, esp with the left hand drive position. I also know somebody who failed because he got mixed up over indicator direction and indicated left instead of right. Although he corrected straight away examiner said it had to be instant fail.
Some good tips in the tractor and specialist vehicle test booklet produced by dvla.
Cheers
Timbo