This sub assembly stage is easy. Place the two bottom brackets under the front bar and square up in position as shown before welding. Notice this assembly is NOT symmetrical, with the space on the left side almost an inch smaller than on the right. This aligns the bottom brackets with existing tapped holes in the car frame goal post. If you prefer screws to welding, make the bottom brackets half an inch longer to come near flush at the front (file or grind smooth). Use flat head screws countersunk to be flush on top. Also maybe use acorn nuts underneath to cover the screw tips and be nice to your passenger.