I am pretty sure that 1 and 4 are flamers, but it is hard to tell with these old models. I have all of them around somewhere but in those early days the plasma guns and the heavy plasma guns had a conical discharge nozzle. But ages ago I did take one of those flamers and drilled more ports into it to turn it into a plasma gun. So who knows really?
They're actually Space Crusade plasma guns. 1 is the SM version, 4 is the chaos Dreadnought version. All bar the RTB-01 missile launchers at the bottom are from Space Crusade.