Recommended valve stem seals

[rlavende]

My '68 Malibu 327ci smokes upon startup, uses oil, and fouls two plugs pretty quickly. Compression is over 155psi in all cylinders, and it runs good. It sat in storage for most of 20 years, so you can imagine the need to replace everything with rubber components. I'm betting valve seals are next on my weekly "battle list".
So, in shopping for seals, I find umbrella, o-ring, teflon, rubber, and teflon/steel. Then I find diameters of 5/16, 3/8, and 11/32.
Please help me pick the best seal for this "street built" daily driver, and tell me how to research the original stem diameter without pulling the covers (yet).
Thanks guys (and Mrs. G)
Rich