Well I guess the answer would be, yes you can, but it will be difficult. It would be hard enough in the first place to get all of the dirt, grease, grime, and rust off the frame before you painted. There is not a whole lot of room between the splash apron and the side of the frame, so that will be a bit hard. If you did not want to take the engine out, I would at least suggest taking most everything off the engine and then clean it and mask it off and then spray it green. You would still have some issues with getting all the oil/grease off. Then paint your items as you put them back on the engine. Certainly painting with a brush will look like you painted it with a brush but if that does not bother or concern you then it will work.