oil filter plate 340

One other thing to look out for is to check the centre of the plate is not bottoming out on the block before you tighten the centre nut. Sometimes (probably due to overtightening) the plate is too "flat" so the centre the nut can't apply tension to seal the outside of the plate. If you turn the plate over you can gently tap the centre out slightly and trial fit it to see if the outside surface of the plate is pushing on the gasket but the centre is off the block slightly.
I don't think drilling the extra holes causes a loss of integrity in the plate, it's quite thick and is not torqued that much anyway, I've read between 30 and 50 lbs/ft. I think I did mine to 40.