Yes, the excellent picture taking us to the lineside makes all the difference! As H. C. Casserley often remarks in the Observer's "Railway Locomotives of Britain", when stuck for "Additional Identification Features", "Most easily identified by Number Series"!
TBH, the only GWR Castle I've ever seen is Caerphilly Castle, when it was in the Science Museum. The experience was enlivened by a former fireman who had brought his family to look at "his" engine and said many interesting things about it in a lovely Welsh accent. It still makes me chuckle to remember his initial remark: "Oh, I wish I had a pound for every shovelful of coal I put through that hole there!"