Thank you Cobalt.
I do have the Felpro intake set you listed, but different a exhaust set from one suggested by Summit. The LT1/Vortec seals do strongly resemble the ones I removed, but I think have a wider inner diameter. The valve stems I measured were about 0.341". I will try to get some precise measurements tomorrow. I don't want to install anything that doesn't fit and end up with a set of seals that can't be returned.
As to the pros and cons of using umbrella seals, I did find two threads on other forums which may be useful for others readers:
- let's talk valve seals - The 1947 - Present Chevrolet & GMC Truck Message Board Network