wilwood problems

Which reservoir are you sending to the front ?
Where are you "capping" your lines?
I like the modulation feel of the 15/16 best .
Some guys have reported that some brake systems demand a 1" or bigger mc, just for adequate volume. Personally I don't think so...... but I ain't all-knowing.
Off the hop I would suspect an air pocket trapped in the M/C between the two braking chambers.
master-brake3.jpg

The primary line is supposed to go to the front brakes. Take a close look: if you cap the rear line so that no fluid can go out, then any air stuck in front of the primary piston will make a nice little expansion chamber, and you can bleed forever and not get it out. Take a look into your primary reservoir, the rear one, and locate those ports. They have to be at the high point during bench-bleeding.