One way to make sure that what you hear about which original grips are correct is to buy the SW Standard catalog, if you don't already one one. It's a reference guide that's fairly close to comprehensive. So much info in it that it might be hard to follow at times, but you can usually find the info you want.
If you want original wood grips, keep in mind that the standard Magna grips will be almost always be serial numbered to a different gun. One way to avoid a mismatching serial number (if that sort of thing bothers you) is to look for old grips that were from S&W, but not originally sold with a gun. These were sold aftermarket by S&W for customers who were looking to replace worn or broken grips. They won't be serial numbered at all, so it will be obvious to collectors that that they're not original to the gun, but at least they won't have conflicting numbers.
You can also get factory wood target grips, which were never numbered, as far as I know. Your 13-2 won't need diamond targets, and that's good because they're a lot more expensive than non-diamond targets. I'm 95% sure you won't need diamonds on you 64, either, because they introduced that model about the time they phased the diamonds out, but you'll want to verify that with your serial #.
