The air filters are simple blocks of styrene filed to shape. The competed unit, conductor's side. Please ignore the derailed truck -sigh- Engineer's side. Note the brass handrail in front. The GP10 was a fun project that took about 25% as much time as kitbashing the engine using the traditional chop-and-glue method.
How To: Paducah Jeeps the Easy Way - N Scale daniel_leavitt2000 has a very nice thread on how to make those level nose geep rebuilds in N scale. Taks a look. Thanks, Daniel. Additional search terms: GP10 GP11 GP12 jeep scratch build kitbash