The blisters are actually just the humps on the top outside corners of the hood. On the prototype, these contained grids of resistors. The fan housing, in the centre, is best built up with sheet styrene: you shouldn't need any putty for this conversion. The Detail Associates part is the fan shrouding only, which sits on top of the raised area between the blisters. On the prototype, when the controller was put into the dynamic braking position, the traction motors in the trucks became generators, producing electricity which was fed through the resistor banks, where it was converted to heat. The fan sucked cool air in through the side blisters, where is passed over the resistor grids, then expelled the hot air up through the fan.
I just checked in my parts supply, as I had about 100 of those Athearn blisters, but I must've put them out in the recycling bin at some time. Most good hobby shops have a supply of these laying around, and you should be able to get a pair for about $.50. If you can't find any, send me a pm - I'm going to my LHS tomorrow and I'm sure that they have some. I can check for the fan, too, if you want. Once you have all the materials, this conversion shouldn't take more than 15 minutes.
I don't know of any CNR Green #11 in spray cans, but there are several versions available in jars/bottles. I believe Testors offers it in both Floquil lacquer-based paint or PollyScale water-based paint, and Scalecoat has a laquer-based version. My favourite is SMP Accupaint, which can be hard-to-find. All of these are best applied with an airbrush, although most of us old-timers managed this task with a brush at one time. :mrgreen:
Wayne