It partly depends on how nice you want it to look.
If you are looking for a real nice job then I would take everything off - starter, manifolds, radiator, hoses, belts, generator, etc and pressure wash it. Clean and paint the small parts at the same time but seperately.
Then I use liquid Tide and mix about 50/50 in a garden sprayer.
Douse it good then let it sit for half an hour. Then wash it again.
Repeat.
Blow it off with compressed air and let it sit for a couple of days.
Then go after it with a couple of different sizes of wire wheel, clean any rust or flaking paint off.
Then I buy a gallon of lacquer thinner and spray it again with the garden sprayer.
First make sure you have no water left in the sprayer.
Catch it in a pan underneath the tractor and use it with a brush to get in cracks and crevices.
Spray again.
Blow it dry. Then I just rattle can prime any bare spots. Let it sit for an hour hour and shoot the paint on with an automotive spray gun.
I never sandblast the main componants of the tractor.
Too much chance of getting grit inside and ruining it.
I should have snapped a pic of this engine before I started on it today.
It was almost black. But 3 treatments of Tide and and an hour and a half of washing has it the right color again.
I have this engine sold so this is all the farther I will go with it.
When the man installs it he wont get very dirty.
No it's not Red but the process is the same.