Not sure if you have the ability or not, but I've done a lot of generator repainting and typically I would buy the green Gillespe 383 green in bulk ( qts, and gallons ) from Rapco parts and spray it with a spray gun, you can get a cheap HVLP spray gun for $25 on line ( can also use a cheap airless sprayer if you don't have a large enough air compressor). Then I would use the brown Rapco spray cans and black rust-oleum high heat from home depot ( $5 a can instead of $14 for Rapco ) for the black. paint everything green, then make negative stencils out of corrugated cardboard to cover the green and expose only the brown, then lastly add more stencils to cover green and brown with just black areas exposed.
Do not tape off the areas you want to mask with paper outlined with masking tape because that leaves a sharp crisp line between colors and looks a little stupid, you're really looking for a slightly fuzzy edge between colors, which the corrugated cardboard stencils recreates nicely.