Yes to both - I make my cable out of 3 pieces of 2 gauge cable with big lugs and heat shrink over the lugs to the cable. If the frame is well grounded, then you can ground it to the frame. The best grounding system is to ground all cables to a central bus bar that then is grounded to the battery; this prevents ground loops and grounded parts being at levels not quite at 0 volts - this causes noise in the electrical system, and can blow ecus and other electronic devices. There have been many reports of cars where the only ground for the engine and tranny was through the tranny, with some cars catching fire due to the poor grounding.