Easy to mark out in a drill press.
Mount center drill in chuck. Slide head on table, figure out a way to clamp lightly.
With camtower on head, line up point on camtower where you want the bolt to bear down,clamp head.
Then slip on cam cover with dowels in place, then drill into cover till it breaks thru, or at least has a good start. Repeat on other 7 holes.
You can use thin spacers, to aid in lifting off valvecover...
Now you are ready to weld on the supports.