No reason why skirts would not have been fitted to one of these Corpet-Louvet engines In fact it would make perfect sense given the use of a tram on your line!
It's taken me a little time to find it, but I was certain someone did a Gauge 1 french 600mm gauge steam loco kit/parts. Got there in the end: http://www.steamandthings.com/fpage27.htm
Just a shame the chassis isn't one of the parts available.