340 block 1969

Take those out. First they are copper and they should be stainless steel. Second, you should only use them with dead soft copper gaskets, not any other gasket although I've seen guys use them under Fel-Pro blue gaskets. I wouldn't do it.

If you are going to build a true 340 (not a stroker) you will probably deck enough off the block to remove the grooves. Either way, I'd deck the grooves out and if I had to, I'd remove a bit off the piston (ASSuming flat top piston) to correct compression ratio if you need to.