If you're getting 1400-1500psi at the MC, you know it's in good shape. Most calipers can't cope with that amount of pressure. The Wilwoods I have caution against pressures above 1200psi. The iron stuff you have probably only wants up to about 1000psi max. Now that you've verified pressure at the MC, you need to verify you have pressure at the calipers. If you're confident you've properly bled the system, take some vice grips and clamp the soft lines just enough to close them without damaging the line, then check the pedal. If it's still spongy and goes to the floor, you have air in your hard lines. If it's rock hard, move your testing to the calipers. Unclamp the soft lines and try the pedal again. If it's spongy and moves to the floor, you likely have air in the calipers.
If that's the case, try out a reverse bleeder.
I have this one here.
https://www.amazon.com/Phoenix-Syste...zcF9hdGY&psc=1
I'll never use another type of bleeding method. This thing is fast, doesn't need an extra person and isn't trying to push air in a direction it doesn't want to go. I had similar issues and this worked for me.
I started by sucking most of the fluid out of the reservoir/s, keeping just enough not to uncover the internal ports. Then move to the various corners and push fluid up through the system, in the direction air actually wants to travel. Typically about 10 pumps per caliper will fill the reservoir back up. As you remove the reverse bleeder, you allow the bleeder port to burp and gravity feed just a slight amount and you're done.
Then test the pedal again.