A few minutes at StewMac got me prices for Tuners and P-90 pickups in US$.

If those tuners are indeed almost 30 years old, the plastic knobs may be fragile, and not very good for regular use. The Grover Keystones look very similar, and are likely to be much better quality. I had an old SG, and those tuners were miserable pieces of merde. The new Grovers would be considerably less expensive, even with the exchange rate, shipping, and taxes. Are you restoring a museum piece, or do you plan to actually play it?

Your mini-humbuckers would be smaller versions of the P-90's, I think. The price comes out about the same as your quote. If it fits your guitar's cutout, its probably a good deal.

Guitar Trader (888-448-4828) is offering 'faded' Gison SG guitars in Brown or Cherry. So I guess you are already there.

I suggest you get hold of someone who can appraise the value of your guitar, to help you decide what you want to do to fix it up. It would be a shame to reduce the value of a sought-after collector's item. It would be a disaster to spend big money on vintage parts that reduce the playability of an instrument that is not particularly collectable. I think it comes down to whether you would rather look at it, or play it!