Most Yugo M59/66s you find will be in much better condition that the "best" Yugo M59s on the market, and somewhat less expensive. Some people have had issue with these rifles — if they have been poorly maintained — as this model's adjustable gas valve can occasionally leak, preventing proper cycling. Spring for a "hand-pick" or "unissued" quality rifle and this probably won't be an issue. But there are also new-manufacture stainless steel valves available for about $25 (scroll to bottom):
http://www.murraysguns.com/sksown.htm
I cut down and re-crowned an M59/66 with excellent results, removing about four inches of barrel/grenade launcher. Accuracy was not affected. However, it may be more time/cost effective for you to simply purchase a Chinese SKS. Here's some info on crowning:
http://riflestocks.tripod.com/targetcrown.html
The best way to scope an SKS is to use a side mount like these from Choate and Kalinka:
http://www.riflestock.com/catalog_page.cfm?queries_index=index10&ProductCode=22&ProductSubCodeID=160&NewProduct=0
http://www.kalinkaoptics.com/detail.aspx?ID=565
Both attach to the receiver and have NO wobble. However, you must drill/tap the rifle for attachment. You'll find basic instructions here:
http://www.surplusrifle.com/reviews/choatesksscope/index.asp
As someone else noted, the Scoutscope system is said to be quite good as well and requires NO gunsmithing or permanent alteration of your rifle. This is something to think about. However, I have not personally used one.
Regardless, the SKS is a great rifle for many applications and I'm sure you will be happy with it so long as your expectations aren't too high. I don't have a Chinese, but have found all others to be of roughly equal manufacturing quality with some minor variation. However, the Chinese and Russians do have chrome-lined bores, which helps with cleaning and wear. (The Yugos do not.)
Here's a great site on the variations between countries:
http://www.yooperj.com/SKS.htm
Just to show off, here are a couple of mine:
Albanian:
Russian:
Romanian:
As you may be able to tell, I have a soft spot in my head for SKSs!