tech-toy bought theirs from z'sondabrain over at classiczcars, and dave built them using rt dimensions with the bends for additional clearance for the brake and fuel lines.
Using the gm mount, it lowers the nose of the differential for those who have v8 conversions. For those of us who still have the l6, we still use the stock diff mount along with a bump stop/snubber and cut it down.