So after 30 years of driving my GMC 270 smoking truck I finally have time to tackle valve guide seals. I found NO valve guide seals or grooves for the O rings. There were six valve lash caps, two are broken. I'm taking a chance here... I ordered universal umbrella seals and lash caps. I spoke to a mechanic younger than me who loves old iron and he said the GMC 270 didn't use oil seals but make sure I use lash caps due to the geometry. My 248 has O ring seals and NO lash caps at all. I figure...what could possibly go wrong??! Either way the smoke should slow down and the worst thing is I have to adjust some valves! Your ideas?

Yes. Have the origial valve guides lined with brass inserts and machine the guides for PC style teflon seals. Your machinist has to be careful and make sure there is sufficient clearance between the valve stem and the seal for some lubrication to the valve stems or they will seize. The bronze liners also hel;p with lubrication. I have been using this style seal on my 235 and 261 motors for 40 years or better.