Mines an 09 plate and has the box section style swing arm,as does my mates 07 plate..both Rs

They are probably both old unsold stock bikes sold later than issued.

see here

I think I may confused the single / twin spark thing. I used to have BMWs and they went from physically having two spark plugs to one (and then back again). In the case of the XT doesn't it just mean lost spark vs one spark every firing cycle (or two revolutions)?
I've got both bikes now and am loving riding them. Plenty of power for the motorway and very good on the green lanes too.
I've set the tappets and changed the oil on both so they're good to go,