I see a big flaw. the pinion support si hardmounted to the frame, and the rest of the centersection is rubbermounted...
and eliminating the longitudinal arm in favour of a rigid mount shows that whoever did the design hasnt done the math.
allow me to demonstrate:
500 ft/lbs of engine tourque, 3:1 first gear ratio, 3.55 rear end gearing = 500x3x3.55= 5325 ft pound of tourque to the halfshafts, and 5325 footpounds of opposite tourque acting on the diff... if teh distance from the halfshafts to the mounting pad is one foot.. then you will have over 5000 pounds of pressure on the pad... AND the same on the rubber in the transverse mount.. the rubber will deform.. and the steel in the mount on the diff will deform .. but the rubber will rebound...
if you guys had retained the longitudinal tourquer arm (that GM engineered for a reason i moght add)
the length of the arm (5-6 feet) would have reduced the pressure on the forward mount to about 1000 pounds... AND the rubber in the tranny to torquearm mount would not permanently deform and also reduce noise over your solid solution...
the rest of the frame looks great though.. but that mount needs fixing