craig ... here's a variation of the hair pin mount;
the piece of 7/8" dom is inserted 3/8" into the frame tube at a 90 degree angle to the hair pin. a plate/gusset is then cut to fit over the tube, flush with the outside edge of the rail tubing. then an oval is cut from 10g sheet to fit over the dom. weld two 1/4 x 20 studs to the back of the plate. this plate will be chromed. i used a '39 ford tail light bezzel for a pattern. just a lil detail.
Ron