Totally agree with the tape I did two layers on the inside also,and when you peel the tape make sure you peel from the outer towards the center "SLOWLY". So what you'll need is a measuring tape,pencil,masking tape,drill,round file and metal cutting device of your choice,personally I'm more comfortable with a 1 1/4" hole saw.
Layer your masking tape on the outside move your grommet until it is equidistant between the two bolts then move it about an inch away from the bolts. Grab your pencil fold the grommet over make a center mark,tape the inside,start drilling. After your done drilling use your round file inside and outside then peel the tape. Coat the hole with oil install grommet. Stand back,smile and pat yourself on the back,job well done.