Spongy/No pedal, air still in system? Bad MC?

[Toro]

After replacing front driver/passenger brake hoses and lines (72 Blazer), and after multiple bleeds, I still have spongy pedal that eventually goes to floor. It won't build up after pumping, just keeps going down. I'm using clear tubing on the bleeders, and first or second bleedings I saw air bubbles, have not seen any air for last few bleeds, but still no firm pedal. I'm also using one of the screw-in tools on the proportioning valve. Next step would be to try vacuum bleed. Any other suggestions or things to try? Also wondering best way to tell if MC seals are still okay. I'm not seeing any fluid around the rod/plunger. And double checked fittings on lines/hoses, they are tight without leaks. Thanks for any help.., I've called it quits for the night.