I am replacing my original valve stem seals on my '77 350 and was wondering what is the best replacement ones to use. I'm not sure what diameter the stems are and I know there are a few different types. Umbrella, stock O-ring.

Which is recommended, where can I get them, and what is the correct size for my stock head. I'd rather go with something improved over the stock O-ring type, but I'm not sure of the best one.

Thanks much.

Umbrella type seem to be better, just about any parts store carries them, and some people will use both. However -- you are replacing the original seals? I'm going to ass/u/me that the heads have been rebuilt to include new valve guides? If not, new seals will be toast in short order...

Going with an umbrella seal including the O ring seal can help to eliminate the startup puff of smoke the Chevy small block (older models) are popular for. They aren't a cure for worn out guides (or rings for that matter) but they will help to reduce some of the smoking and oil consumption if the guides are loose. A worn out guide will not damage an umbrella seal, but it would damage a positive seal, but your heads unless modified from stock don't readily accept a positive seal.
Beware that not all SBC heads of that era had the same valve stem diameters for both the intake and exhaust. If the heads were off a passenger car they will both be 11/32 diameter, if they came off a truck they will have 3/8" exhaust stems.
You also have to make sure you have enough clearance to install a valve seal, as in you need .060" more seal to retainer clearance than the lift of your cam.

Thanks for the information guys. I'm assuming that my guides and rings are ok, as the engine has only 29k original miles on it. It does have that puff of smoke upon start up and I'm thinking it's due to dried out stem seals with such low miles after 30 years. I guess I'll find out. If theres no improvement, I'll pull the heads and have them reconditioned.

Adam - to put it shortly, unless you have another problem, I'd live with a short puff of smoke. Replacing seals means removing valve springs, a job I don't particularly enjoy with the head on an engine. There is an old saying about older SBC's and Radial Aircraft engines; if they aren't leaking, they are out of oil... IMHO