It's not a pool of oil to worry about...it's oil flying everywhere when the engine runs. Install a clear plastic valve cover and observe!
The engines with boots did not have an O-ring.
Knurling the guides was a way to save worn guides by changing the diameter.
My old 71 Chilton's shows them both; O-rings on some sixes and SV8, and "boots" on large V-8s.
The top of the valve guide can be machined to use the newer style seals.
