Hi mate. Welcome to the world of owning a bike that the local dealers usually have no knowledge of.
Regarding you fork seals, as I stated on your thread on the US site, you'll have to order seals to fit an 81 RH as they were marketed here, and your local Yam dealer will have a listing for them.
Here's a link to a previous thread -
CLICK, that shows all the other XS11's that use the same size seals. Very handy if you're ordering them online, but just get the seller to verify the actual size before hitting the "buy" button, as many of them have no idea what they're selling.
I've had my SF since 2001, when it showed a very modest 18,700 odd klms and have had an extremely good run out of it.
As for the buckhorn bars, I can't comment on them as my bike was fitted with RH bars when purchased, but from chat on the US site about them, it depends a lot on the bikes' intended use and how tall you are.
Mark (boss.0427), owner of the only other 79 SF that I've laid eyes on, who I met at the last rally said he found them pretty good, so it'll be down to just what you feel comfortable with.
The range from the little tank can vary considerably, depending on how fast you want to travel. Back in my days as a Brisbanite, main usage was traversing the array of mountains and great roads around the hinterland averaging between 80 - 100kph and the bike used to pull 220 klms before reserve was needed, which equates exactly to what Mark stated his SF returned out of his. However, once I moved up to the country and average speed ids up over the 110 kph mark, range had dropped to about 170 before reserve, so if you play you pay.
Unfortunately, you won't find a Manual specifically for your SF, unless to chance upon a factory Yamaha one from the states, so your main options would be either a Clymer or Haynes, both of which have a supplementary section to cover the Specials.
Have a look at the US sites' Catatonic Bug's webpage, as he has a number of manuals online there to download for free, though there's nothing like having a book on the workbench with the page open at the section, while you're working on your baby.
Oh, and one last thing, don't freak out when you see your front brake pads for the first time.They are supposed to be angled like that.
