On 11th August SAS have a sale of trains which includes three Gauge 3 engines. All look be to be very nice and their estimates are extremely low, even allowing for the usual caveat that boilers may not have certificates etc.
The Duchess is an updated Bonds design and has four cylinders
http://www.specialauctionservices.com/large/tg110816/lot0451.html
The A3 is an MAP design with three cylinders
http://www.specialauctionservices.com/large/tg110816/lot0452.html
The Grange is also from the well know design published by MAP
http://www.specialauctionservices.com/large/tg110816/lot0453.html
Mike
Just for the record, the Duchess and the A3 both sold for £3800 each and the Grange £1900. I assume that's plus 18% commission and VAT.
Mike