The Stovebolt Site Forums The Shop Area Engine Shop viton umbrella or sheet metal shield valve stem seals

I am rebuilding a 1961 235 848 head (C10 truck). The guides are magnetic. So, I guess they are cast iron, probably original.
One intake guide is broken. The broken piece was stuck to the valve stem in the combustion chamber. Had to hammer out one intake and two exhaust valves.
The head was last "reconditioned" at a shop in 1979, has about 73k on it with positive stem seals (see no evidence of O-ring seals).
Am considering Viton umbrella seals -or- O-rings with the sheet metal shield.
The O-rings are easy to source, but where do I source the shields? What is the proper search term for these things?
I assume the O-rings are just rubber.
Viton is attractive due to its reputed durability over rubber, but where do I source this for the 235?
And, of course, I want proper lube to the valve stems if a Viton option is available.
Has anyone a source for either the shields and/or a Viton option?
The head is going to a shop to at least replace the broken guide and inspect/clean the head and seats.
Thanks.

The machine shop will have the seals the head needs, if not find another shop. If the guides are sized correctly, a Viton positive seal will be your best option, but due to the better sealing capabilities of the Viton material and the positive seal, the guides have to have the correct clearance. Guides need some oil to lubricate the stems, the trick is getting the correct oil for the clearances you have.