No magnets for me since I used strips. I used a steel drilling jig I made that matched the receiver hole pattern locations and drilled the flange for the receivers. Drew a line and marked 2” from the hole and marked the drill spot on the cowl 2” from the reference mark. Since I couldn’t see thru the carbon fiber strip, drilled first with a #40 bit and wallowed out the fiberglass hole since glass is softer than aluminum. Then drilled it round with a #30 And put a cleco in it.
For the sides, using what I learned about predrilling the flanges before fitting the cowl, I will drill a #30 pilot hole thru the cowl and flange for a perfect match, and then using the jig, drill the receiver rivet holes In the flange. Had I known this before, I would have done the firewall flanges this way and saved a day’s time Instead of trying to hit the hidden flange hole thru the cowl.
When it comes time to drill the large holes, I will unibit both cowl and flange together with a 1/2” bit, then remove cowl and finish both holes with a larger unibit. To ensure the cowl doesn’t move as the big holes are drilled, I will drill between the Skybolt locations and use a temporary #40 cleoco, filling in the extra holes in the cowl afterwards.