Mark,
Many companies sell the cast iron grey paint which works well.
as far as the cleaning goes, I lay a large cardboard or carpet scrap on the ground under the vehicle. I get 5 gallons of deisel or kerosene, use a sand blasting gun and put a hose from the gun into the kero and give everything a good soaking then poke and scrape at the thick stuff and spray some more. after it has soaked a bit spray it down as though you were sandblasting it, then blow dry everything with air. Wear a mist and fume mask because it really vaporizes the stuff and don't smoke around the fumes. If paint isn't an issue and you want to topcoat with paint, I give the final rinsing with laquer thinner to remove any residue, it dries quick and paint will adhere better.
They sell a cheap generic sandblasting kit at wal-Mart and other places for like $12.00. You may want to restrict the hose size or you will go through some serious fluid. I restrict down to like a 1/4" clear gasline hose like used on snowmobiles.
Then take the oil and kero soaked card board and start your bonfire.

55 Vicky & customline
58 Rack Dump, 55 F350 yard truck, 57 F100
59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?