They do have a selection of in house builders. Not a gang you understand just the odd one or three or more.There's a comment somewhere that they were made by the guy at GRS. [Though there were a lot of them, so I don't know how he'd have time to build them and run a shop!] And they do look nice in the photos.
I had 2-6-2+2-6-2 Garrett that I foolishly bought from a guy in the UK (couldn't sell it in the USA when I got fed up of it: no-one knew what it was.) Same kind of construction - the power was a pair of LGB 2085 trucks.