These umbrella seals where going to last me "forever" according to the guy who did the heads. Any idea what happened to them? They are not hardened or cracking, they are very flexible and hard to tear. I'm not removing the heads and having them cut to hold positive valve seals, so I'm installing the old fashioned umbrella seals that I got with a gasket kit from the rebuild. They worked OK before.
Now that I got your attention, any tips on how to get the valve spring off of #8 exhaust valve without cutting a hole in the firewall? (BBC) #7 intake was a challenge but I got it using a spring tool that looks like a special crow bar. It was cheap so I'm thinking of cutting it and welding it so the long end is at an angle and misses the firewall. Yes, the more I think of it the better that sounds.