[alfaloco]

Does it have a vacuum brake booster? If so, it may be that the pushrod inside the booster is just slightly pressurizing the master cylinder because of the spacing between that pushrod and the master cylinder piston rod. Did you replace the master cylinder with another one?
Or replace the booster?
Trapped air can do this as well, if the brakes are not bled completely.

 

[alfaloco]

OK-- yes I had this issue with a Suzuki sport bike years ago, with twin discs up front. I traced it down to air trapped in the hoses. Kind of hard to bleed it out when the master cylinder was much higher than the calipers.
It doesn't take much of an air pocket, because as you know when you heat air, it expands. Bingo-- pressure on the pads.
Check the reservoir also to ensure it's well seated on the rubber seal where it pops into the top of the master cylinder.

 

[alfaloco]

Will brakes can be a mystery! they have mystified me a couple of times.

 

[alfaloco]

That's easy enough to do, and worth trying IMO. Assuming there's no adjustment on the pedal travel.

 

[alfaloco]

Your brake hardware is fine. The bleeders are upward, which is correct. I really believe you'll find the solution via the master cylinder, or the brake hoses (but you say they are new, so unlikely they are the cause).
Take Greig's suggestion and jack up the front once the brakes are hot and dragging. Test the rotation of each wheel. Crack open the bleed fittings and see if you get a little spurt of fluid, and then the wheel loosens. If that's what you see, the master cylinder is not releasing pressure applied to the pads, or something downstream of the master cylinder (like old brake line tubing, with some crud inside??). You may have to readjust that pedal clevis again until the internal piston clears the inlet port from the reservoir.

 

[alfaloco]

Biggs, I still think the solution is in the master cylinder adjustment, but something you said in post 19 concerns me also. You said the "brakes were seized", and you indicated you rebuilt all 4 calipers. It is possible that we have more than one gremlin here, if the pistons were seized in the calipers, maybe corroded, that's not going to give you consistent brake action.
Anyway... I am with the others here, adjust the master cylinder pushrod a bit at a time, see what results you get. AND check the fittings and line down from the fluid reservoir under the hood, also. Make certain they are tight and not introducing air into the system as you operate the pedal. If a hydraulic system can suck in air, it will do so, believe me.

 

[alfaloco]

I gotta love that lead in line, Biggs... "Hey guys may have had some break through here. "
But yes, I'm with Greig and the others here on the M/C. But I emphasize again, the second paragraph of my post 34, check the inlet side of the M/C also, from the fluid can on down to the cylinder fitting. That includes the vent hole in the cap.

 

[alfaloco]

Here's a photo of the hardware I used on my recent brake rebuild on my Spider. It appears similar to what I see in the photos above, and came through Classic Alfa. But the spring will only fit one way, because the curvature in each end is meant to apply pressure to the pins, and allow them to be inserted through the assembly. Once the pins are inserted, they maintain the spring in position. What's shown in the photos is how my calipers went back together, and there were no issues with them at all. I think if you tried to flip the springs over, they might even rub the disc. On the OEM spring, notice the rub marks in the curvature where the pins pass through.