can someone help me with plug selection

You can buy a gapping tool at the parts store that you get your plugs from. The easiest way will be to use it to measure the gap on the plugs you remove, and gap the new plugs to the same measurement. It will pretty much explain itself once you get the tool.
Brandon
 
once you see the gap guage you'll understand, or get someone at the parts store to show you real fast. basicly the gap is the distance between the ground strap and the electrode, you want that to be at .054'' on a stock 5.0