I used the extruded piano hinge method to join my engine cowls for my Viking 110 engine. The attachment method to the top and bottom cowl and the firewall went well. The stock pins (.089) would not fit the bent hinge, but the undersize pins supplied by Viking (.078) fit.
After painting, however, the .078 dia. undersize pins did not fit in easily. Without a really long drill, I looked for pins that were smaller dia.

The pins should be hard drawn, corrosion resistant and available in at least a 30" length. My best solution is using drawn steel TIG filler rod in .062 dia. and it is copper plated for lubricity and corrosion resistance. This slides into the piano hinge sections easily and is strong. TIG filler rod is also available in hard drawn Titanium and .055 drawn steel.
Happy building and flying