When I took my heads to the machine shop, I told the machinist it was likely the guides would need replaced as they felt rather loose. The heads have 270,000 miles on them. I bought new ferrea valves along with new springs and etc. I asked him when I picked them up if he had to replace the guides, he said "no, they checked good, we check them using a vacuum method, if it holds vacuum the guide is okay" I never heard of this method, and I`m not about to throw this thing together to have the guides leak like hell and have to take the heads right back off, It`s hard for me to believe the guides aren`t shot after 270,000 miles. However when I did remove the heads, they showed little sign of oil on the valves, even so the valve seals were hard and brittle, anyone want to offer any insight on this?