If you are running it in a magnum factory EFI aplication you have to use a similar one for the tone wheel. However, that one in particular is for a V6 and will not signal the V8 computer properly anyhow but is built the same as the 318 plate otherwise and the 318 plate is the same as the 5.9 plate minus a big weight welded on one side.

I would not wory about it as far as strength, with all the extra metal around the perimiter it has to be a lot stronger than the old factory ones on 340s or even 440s and such.

Those balance holes look factory, I have seen tons of those flex plates and some have few or no holes and some have a bunch like that one, it is just to get it to a neutral balance. Stamped sheetmetal is not something that tends to come out balanced very well without some extra effort.

If you really feel the need to replace it with something else AND it really was really balanced with the rotating assy, a competant machine shop could see what the balance factor is on that plate and balance your new plate to the same spec. However I think the only out of balance they may find is a few grams that would have been within the factory "neutral balance spec-range of tolerance".