first, the cheap plastic Century stocks (both butt and handguard) are US parts, so swapping them for wood will make you uncompliant according to the feds. A US made magazine (thermold makes a good one) will offset that with 3 US parts which would also allow you to put on a FH if you wanted too or swap P-grips as well if you wanted.
For swapping just the stock and keeping all the same metal stuff, pull off the buttpad, and there is a long bolt inside (flathead). pull that bolt out, and in most cases, with plastc buttstocks, there will be a sleeve spacer on the bolt that wont be used with the wood. HOWEVER on some Century rifles, they cut and rewelded the bolt to length and if that is the case, the bolt is WORTHLESS for a wood stock. You'll still need to buy a rubber buttpad, and figure out something to go in the pin holes if you want metal in there. A guy a while back had some brass inserts, but I'm fairly certain he is all out, and I dont know of any other source.
Honestly I think your best bet is to buy a complete stock set recoil assembly and all and go about it that way.
http://www.gearshanty.com/shooting-1.htm He's got 1 available, and he's a great guy to deal with. Keep in mind that it will be USED and not "new"like the tapco new spanish stocks without any metal. It will probably need to be refinished, but its worth it if you ask me to get the whole recoil assembly for $15.
Also, you could get G3 wood which will fit as well with minor modification to the spring retainer on the end of the recoil spring.