Above is the underside of the Jeep mold. The thing in the center is his attachment point to form Bruticus. If'n you wanna add one, there should be plenty of space under there if this configuration is used.
The Hound mold has that plastic piece that connects the lower torso to the upper chest/fenders/hood. Make two diagonal cut to this and glue a layer of styrene to the lower section of this connection point. Then, use a screw on each side of this joint to allow it to pivot. How high you make the cut will determine how high or low his chest sits. The original molds entire fenders were removed right under the hood line straight across to the door opening. Leave the factory door pins in place.
The head just rotates and become a center council-like thing and the seats need to be cut around it to fit when in Jeep mode. The dash board is out of a 77 CJ Jeep model kit and has the neck ball joint connected to it. The steering wheel swivel was used on this and swings out of the way but gets in the way when he forms Bruticus so I had to remove it.
The Jeep mold rocker panels remain in place but are notched out to allow the Sideswipe rockers to snug up in there. Once the Viper mold rockers are into place under the Jeep rockers, try to blunt-off the end of the pins to keep them from falling off. Once you get these new arms swung into place within the Jeep mode, build new fenders for him, then build the hood the fender extensions to fit them. (Picture 1, written in purple)
Extras to note:
The seats are hinged on the lower torso to put them on his back in robot mode. They both have a little round thingy on them which allows the spare tire to clip onto.
The windshield has new hinges to allow it to lay forward onto the hood.
The grill is hinged further forward than usual to keep the arms hidden underneath. It also keeps the grill from binding with the hood when forming the waist.
Hope that helps.