My bows are stainless steel from Vintage Speedsters. I made threaded inserts from 1/2" OD aluminum round bar. They are about 1 3/8" overall length with 1" of length turned down to 7/16" diameter. The 1" long, 7/16" diameter slips into the inside diameter of the bow tubing. The inserts are drilled thru and tapped 5/16-18NC for the rod ends. I epoxied them into the bows using JB Weld.
The rod ends are 5/16" stainless steel rod ends from McMaster-Carr (not Heim style rod ends, although they could be used)
Align the hole in the rod end with the existing hole in the bow, leaving room for adjustment, mark and cut the bow, deburr and install the threaded insert with the JB Weld.
Hope this makes sense!