I used a caliper to compare the skin+firewall flange to the cowl thickness. Using that as a judge, I used no shim along the bottom (due to the thick bottom skin) and 0.16 along the tops and sides. I didn't think about the undersized hinge pin along the top. I may get the same bulging problem.
I haven't riveted everything together yet, so I'm not sure how it will work out. Seems pretty good at the cleco stage.
Dave