If the pedal remains hard and has no fade its definetly needs burping again, and again, till you get it all out. All them pistons can trap air and can be stubburd to bleed.
The method that works best is to hook a small rubber hose off the bleeder screw and then submerge the hose in a bottle of brake fluid ( a old coke bottle works good but any clear bottle will do. Next open the bleeder screw and then slowly cycle the brake pedal all the way then release repeating several times till you have no air bubble present ( requires another set of eyes) in the bottle.
I would save your money on a wilwood M/C and get a later model GM quick take up master cylinder, they work just as good or better as the pricey wilwood units.
JMO> Charles