No Tab Screwed to cowl approach
I made a small loop in the end of the side cowl hinge pins for inserting and removing with a tool made of hinge pin wire. Then I made a notch in the upper cowl half at the location of pin loops when fully inserted so they could go below the cowl surface at this location. I made up two covers of the thinnest aluminum I had available (I think it was .016 2024T6) for the modified area of the cowl. Think of an long narrow triangle with well rounded corners on the two equal angles and a disc on the long pointy end. With the appropriate care I determined by trial fitting, marking and drilling the mounting hole in the disc area. This went inside the air inlet of the cowl in the separation area where the two cowl halfs are overlapped. I held it where I wanted it on the assembled cowl and marked the exposed upper cowl surface with a sharpie pen. I disassembled the cowl and drilled a hole in the marked location, then reassembled the cowl and used the hole in the upper cowl for marking the now exposed underlying surface of the lower cowl, then disassembled the cowl again and drilled the mating hole in the lower cowl. In my first approach I riveted a platenut directly to the inner surface of this non-honeycomb area of the cowl but I later riveted an aluminum strap to the inner surface of the lower cowl with the platenut mounted on it - the short edge distance on the lip of the cowl just wouldn't stand up to the installation and removal loads. The same care and alignment is required for locating the plate nut on the aluminum starp but a floating plate nut in the final instalation assures there will be no stresses other than compression upon assembly and in flight. Once the inner assembly is complete the outer work is pretty simple - just wrap the thin cover around the leading edge of the cowl covering the cowl separation line and the pin loop notch and lay it down the cowl with one well rounded point above the split line and one below. When the hole locations are determined in the cover corners they can be removed, drilled, reinstalled and used as a drill guide for drilling the mounting holes in the non-honeycomb area of the upper and lower cowl halfs. I mounted platenuts inside the cowl halfs at these two locations and they work just fine as is. There is a lot of subtle stuff about doing things in a specific order to retain alignment precision, oversize screw holes for stress relief that were an aquired knowledge by this point in the building process. The cowl surface interfacing the cover is countersunk at the screw holes and the thin aluminum cover is dimpled at the screw holes. This approach smooths out the leading edge of the cowl at the separation line and it takes the airload off of the hinges along the side separation line in flight. There are several other approaches to getting rid of the square tab screwed to the outside of the otherwise slick cowl that are more elegant such as inserting the pins from inside the cockpit and securing them there. It is one of the things I look for on most every RV I look at - how did the builder deal with the side hinge pin installation. Mine is the the blue/red/white RV-6A shown as RV of the Week #9 I think and you should be able to see the shiny cover plates at the front of the cowl. I have argued with myself both ways about painting them. For now they are clean for serviceability. Anyway, this was my approach to dealing with the side hinge pin problem.
