Clamped the lower cowl in place with sheet metal clamp sand a ton of painters tape. Then back drilled through the piano hinge halves from the inside with a 90 degree dotco. Once I had the lower in place with piano hinges on the aft side and clecos into the prop fixture on the front, I spent a couple of hours opening up the horizontal seam to a consistent gap on both sides. I started by running a metal double sided nail file in the seam, then finished up with a piece of adhesive sandpaper stuck to a piece of .020 aluminum. This resulted in a gap of about 1/16" overall. I still need to trim back where the lower butts up to the firewall flange, but it's good enough to get the fasteners in. Once that was done and I was confident it wasn't going to wiggle around, I spent quite a bit of time laying out the pattern for the horizontal line of sky bolt fasteners on both sides. I ended up with a 3" spacing which seems like it will work out nicely, but required that I trim 1/2" off the Flanges. Skybolt says that you should elevate the flanges .20-.25 so that you cant see through the seam, but that would end up with the rivet line only having about .25 e.d. on the fiberglass cowling, which doesn't seem like much. I fudged this another 1/8" and ended up with an overlap of about 1/8" and a e.d. on the rivet line of about 3/8" I trimmed and laid out the holes in the flanges and used them to back drill the cowlings from the outside. This was an easy way to do it, but if you go this route you have to take utmost care to use a drill stop and make sure you know what's back there, because it would be really easy to hit something vital like a valve cover. anyway, got everything trimmed, fit etc. will drill the grommet holes in the upper cowl tomorrow, cleco everything together, do any final edge adjustments and hopefully wrap up this part. I know I'll need a bunch of fit/finish work to make this pretty, but I'll be happy to just have it functional and ready to go for now.