Hi Tom
According to Peter Dobson's book "16mm Live Steam Model Locomotives Vol 1" 1985 (there was no volume 2), there were two Steamcraft Double Fairlies. One was as Jay has shown and the other was a model of Merddin Emrys on the Festiniog. It had two twin cylinder power bogies which were slip eccentric. It was 16" long, 4" wide and 4 7/8" high. For 32mm or 45mm gauge (not convertible is suspect) and min radius 3'6".
Price in 1985 £833 or £950 with radio control.
Cheers
Chris