So I was talking to a friend and he said there was a kit out there that was able to do this. I was thinking from what he was saying this would be cheeper to do than anything else I have heard about, I know it wont be a real G36 because it would be a 308 and not a 223. But the point I was trying to get across here was , is it functional and accurate or just not worry about it .

There is no such kit.  A G3 is a completely different operating principle. Your friend might mean an SL8.

Never heard of, or seen one.

Not possible. There is not one single common part between the two guns. They dont even look remotely similar. One is an all steel delayed blowback/roller 7.62 rifle, whereas the other (G36) is a mostly plastic gas operated 5.56. Your friend is either referring to an SL8 conversion or is smoking dope... The SL8 conversion requires more than just installing a kit. It takes a good bit of work and then, it still does not look like a G36 in my eyes.