Tri-motor engines were radial, and though they do look a little WWI-ish, I'm not quite sure it's a plane engine... looks great so far though, whatever it is!
I have got some proper filler, but I find it takes absolutely forever to get anywhere with it unless it's quite a large area. Need to see if halfords can mix up the proper paints too, RD9, WT3 and BU8. Halfords paints are great for plastic kits, leaves a perfect finish without any polishing.