Whoops, that's what I get for not double checking my sources! That's right they were 0-6-6-0s, perhaps I was thinking simultaneously of the 2-4-4-2 Mallet that is my pfp and the ACN&R Co Mallets. Pity to hear that Mallets don't handle your track very well and I understand your feelings on the Garratt. Still though, there are plenty of other conventional engines on both those railways! I'd do it myself but I have my own (non-lego) model project to finish first.