HG is easy on a 5.0. Buy a chiltons and go step by step and you are good to go. Should take a day if you have the tools. Make sure you buy ARP head bolts or studs though.
First off though, make sure its the HG, could be the valve stem seals leaking. Leakdown test will pinpoint which cylinder(s) have issues though.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.