Well, I just want to find a seal that's like the others. It has a tight fit on both the valve guide and the valve stem.Robert,
Its pretty much catch-as-catch can on the F135s these days. As you noted, there were both 1 and 2 groove valves/keepers on these early heads. And stem seals? Whole nother ball of confusion.
The last NOS engine set I had from Mr. T had O rings for valve stem seals. And I’ve seen a LOT of different seals come off these heads over the years. One set I got from the dealer looked like faucet washers!
As @Splangy would say, ‘if it ain’t broke...