Used a jig saw and a few 1/2" holes in strategic locations to cut out the center section of the rear spinner bulkhead as outlined using the doubler plate. Clecoed the two pieces together, then used several files to deburr the interior edges and match the doubler plate to the bulkhead.
After all edges and holes were deburred, scuffed with scotch brite pad and cleaned with acetone, the primed with SEM. After priming, cleaned the rivet holes and started riveting the doubler plate to the aft side of the spinner bulkhead with AN470-4-4.