Steve, there seem to be more altered ports than stock ports out there, that might account for the various sizes seen on the shelf. It is my understanding that the ports were 1 1/8" for both Rapide and Shadow. As mentioned above, the carb and stub were 1/16" larger on the Shadow.
Also, I read somewhere, probably in an old MPH, that US destined Shadows often were at 8 to one CR, UK and others at 7.3 to one. Apparently the US had higher octane fuel available at that time, so the 8 to one bikes could make use of it. Compression ratios varied greatly depending on where the bike was being shipped to for sale. .My Oz Rapide went to Malta when new. The fuel available there in 1947 must have been awful, the factory set the engine up with 5.9 to one compression.
When I was shopping for a twin in 2003 I asked Pete Gagan if there was much difference in performance between a Rapide and Shadow. He replied " After the first rebuild there isn't!"
Glen