Honestly, I'd just take it to a mechanic and have him do it along with the other 7 an bend over for the bill. There are too many things that can go wrong here (x8). If the plug threads get chewed up or stripped, you'll find yourself in a whole other world of hurt.
BTW, that engine looks like it has a lot more than 75,000 miles on it. Did you happen to verify with a carfax? If you bought it from a dealer and they advertised it at that mileage and find out otherwise, I'd tell them to give you your money back or they'll get sued after you call all the news stations to do an investigative report on them and a police report for fraud. It is too easy to swap out the speedo clusters on these rigs.