Use impact sockets and impact extensions. The 5/8 is correct. Take some digital pics of several angles of your engine to refer to on reassembly as you may not remember where some things go if it takes you 2 days. If you have not already replaced your ignition wires you may want to do them now. Use Magnecore 8mm wires. I had no problems with the headbolts using a 24" breaker bar. They were tight, but came loose with no issues. Clean your surfaces with a 1 sided razor blade before and use RTV on both sides of the valley pan end gaskets.