Meljet missing engine textures & model variations

First can I congratulate Melvin on his superb 777, which I am enjoying. However, I am suffering from missing engine textures on some models- eg UA; some BA models. Others are fine. I have maxed out all settings to no avail..Secondly, how do you get different engine models to show up? At the moment, all my models have P&W engines, even the BA ones, that, on closer inspection, have "RR" textures on them! Do you have to d/l the paintkits to get the different models to show up? What are the painkits for and why are they such big downloads if they are (presumably) texture-free?Many thanksM