According to this article (and my knowledge, lol) the stock rocker arm ratio of most stock small block Chevy's is 1.5:1. Polylocks should work just fine. Whether you need the guide plates is completely up to what type of roller-rockers you get. If they are non-self aligning (NSA), you'll need the guide plates. If they are self aligning, you won't. My recommendation between the two is to get the NSA type and run the guide plates. The self aligning ones are very noisy. Also, if you go with guide plates, ensure you get ones sized to fit your push rods. You don't want a lot of slop between the guides and the plates or it defeats the purpose.
If you are getting the roller-rockers and don't know how to tell if they are self aligning, here are some images of the two types:
If you look at the tip of this Scorpion rocker, you'll see what kind of looks like o-rings between the roller tip and the body of the rocker.
Here is a side-by-side comparison of the same rocker with the one on the left being self-aligning and the one of the right NSA. You can see the small tabs which hang down on either side of the roller tip on the left and the right without. There may be other "types" which will keep the rocker aligned, but this is kind of what you'd be looking for.