A "Woolwich" can be made up from one of the Southern Railway "N" class 2.6.0s - just remove the "blinkers" and drop it into a bucket of dark grey paint! (Or lined green after 1946).
As far as a Dean Goods is concerned, if it is to fit into a Sligo scenario it has to be a loco of MGWR origin ideally, though obviously WLWR & GSWR types came in off the "Burma Road".
The cab of a Dean goods is unlike most that the GSWR or MGWR had, but is not at all unlike WLWR cabs. A simple repaint will turn it into a very generic WLWR 0.6.0; it could, for the sake of argument, given a round-topped firebox and alterations to the front splashers, be turned into one of the two 235 class - but they were scrapped in 1927 & 1951.
Alter its cab to a more GSWR-ish style - a simple job with plasticard - and it's good enough as a generic loco off the Burma Road - one of the many iterations of the J15 class.
I have seen a picture of a MGWR J17 with a cab a bit like that. This would work, and would be arguably more suitable, as these would have been more typical in that area.
The only "must" would be the removal of the brass GWR dome and to put the safety valves in the normal place instead of on top of the cab.
All 0.6.0s would be plain grey up to the mid-1950s, some with flying snails, others not. Towards the last few years of steam, a small number of 0.6.0s were repainted plain black - again, some would acquire flying snails while others didn't.