Hi Dutch yes the 1947 longstrokes didnt have a hole at the bottom of the timing cover therefore crankcases and timing covers are different to the 1948 onwards type.
Hey KiwiGF I recon you can never have enough BSAs. I have actually ventured into Ariels in the last 6mths. I have a disease I cant help it. I was restricting myself just to BSAs but I used to belt around in the mid 1970s on Ariels with a mate of mine so my disease just cant be contained.