jerryl--
I can't speak for the Blueline BB, but I know that in reading a review of the Genesis BB in MR NEWS some months back, that the ABSOLUTE reccommended minimum radius was 22", with a more comfortable radius of 24". The reasons given were the length of the loco, the possibility of the cab and front of the tender hitting together and the rigid rear truck of the Centipede tender--it's a 4-10-0, and only the front truck swivels.
My opinion: That's an awful lot of loco length, even with the double-articulation, to be traversing that tight of a curve. You might be able to do it with the USRA 2-8-8-2, but remember, the Big Boy was the LONGEST articulated steamer ever built in the USA.
Wish I could give you better news,but IMO, the length of the loco, PLUS the rigid rear truck on the tender is going to give your friend a lot of problems.
Tom
Tom View my layout photos! http://s299.photobucket.com/albums/mm310/TWhite-014/Rio%20Grande%20Yuba%20River%20Sub One can NEVER have too many Articulateds!