As these are plastic you could cut back the broken mounts to the 2 remainig boiler plate attachments shown (they will pull out) and the remaining lamp base and clean up/file to straight flat edges to bond new plates to. Fabricate 2 new side plates from (scrap ?) 20/30 thou " plasticard. Bond in place with a decent styrene/ABS solvent adhesive, not CA, epoxy, etc'. Paint matt/satin black to match in (or even use black plasticard instead of white). Job done. Note - you have used pictures of both Shay and Climax, different style mounts - I have 2 of each loco type here, both later series like yours. Hope this helps, Max