As above, the newer guns have CNC fitted plates, but even then there's a problem.
First, the plate still has a little final hand fitting which means that plate will have gaps and mis-fits on a different frame.
Second, when the gun is being built, the side plate is bolted on the frame with special bolts when the gun is being polished.
This means a different side plate may be higher or lower in the frame due to individual hand polishing.
This will mean the plate will either stand up out of the frame slightly, or it will be below the level of the frame.
Either way, it looks like ****.
Since you have an early model with got a lot more hand fitting and more hand polishing, a different plate is very unlikely to fit well or look good.
You have two options:
Buy a used plate, if you can find one, and just hope it fits, or send the gun in to S&W and have the professionals fit a new plate for you.
When buying an older more hand fitted plate and trying to fit it to a different gun, it's probably not going to come out looking like it belongs on it.