I still think not enough psi is reaching the corners. I also dont think the 1&1/32 bore is a problem. a 2000 psi gauge hooked to the corners would ans that (I have one & it was cheap). you know what I would do, just me I would run some parts house prefabbed 3/16 line from the MC port next to the firewall to a brass inverted flare "T" then run both outlets to the front discs (with the other MC port capped). with it bled out if it wont lock em it'd have to be the calipers (one or both) or the MC. those lines are pretty reasonable as are the fittings & you have been comfortable with the fabbing you have done so far in diagnosing this