SoupedUp,
I believe you have it the wrong way round. If I remember correctly, the early Pagodas had the spare, sort of upright and the later models had a bigger fuel tank and therefore a spare horizontal on about a 6 inch post.
My first one, a 65 230SL had the upright spare and the next two, a 71 280SL and 67 250SL both had a bigger tank(80 litres IIRC) and a flat mounted spare on a post, raising the wheel a few inches off the boot floor and moved over to the right.
Regards
Chris