Degreeing a Cam, or not.....

I’d pull the rockers off the drivers side, along with the spark plugs on that side, and take the readings off the pushrods instead of at the valve.

If your cam is in 8* or so retarded....... it should be corrected IMO.

There is another thread here where someone is running that same basic cam(XS282S) in a flat top 446, same heads, in a full bodied 66 Coronet 500 with a 10” converter and 3.73’s, and with only a few outings at the track has already run 11.55@117.