Just be careful, if I recall correctly the factory ones are not rod, etc. welded, rather they are spot welded, so if that is the case be careful not to warp the flex plate as you remove it. If rod, etc. welded, just be careful not to grind anymore than necessary, otherwise you will have an off balanced condition.
There depending on the year, there are magnum flex plates with and without weights, mags were externally balanced, but some with the weight on the flex plate or alternatively weights on the the converter.
