I used 8 awg from Maplin, when I made my earth bonding kit. To be honest, I think that was a bit overkill. 10 awg should be fine and will be cheaper. Just for reference, I cleaned up all the old earthing points I could find and after reassembling, covered them with a coat of Waxoyl, to prevent future degredation. I ran a lead to the alternator, head, block, inlet manifold and another one from the battery to the chassis. You might want to reinforce the MAF and fuel pump earths at the same time too. It's very worthwhile, you should notice slightly better response, fuel economy, idling and your lights will be brighter too !