Ed, it really is pretty easy. First find the center point of the axle and the outer most points you want to go to on the axle. Then keep spliting the difference to make the spacing even and so you have the same amount of holes on each side. Find the right bit depending on the width of the recess in the I-beam that will look right. But before drilling the final size holes, I drill smaller pilot holes so my final bit size doesn't wander. You could practice on a scrap piece of styrene to get comfortable with drilling the holes before doing on your kit.