Oooooooooh, to me that is more fun than a Caddy/Hemi! Does rust = nostalgia? Anyway there is the real world of metal and gooey rust as compared to the old images in my head but I would just check the crankcase oil for chocolate milkshake evidence of water and if the oil is oil I would flush, flush and flush that wonderful old engine till the water runs clear. There used to be a formulation called "Oakite" that was used to clean out rusty blocks but I don't know where to get it these days. Since rust is an oxide and oxides are bases in water, the vinegar will do the most good since it is a weak acid and can dissolve rust. A caustic or basic flush will not do much good as far as cleaning our rust; a mild acid is needed. If vinegar does not meet your idea of a clean block the next step would be to use oxalic acid but drug store muriatic acid (HCl) is too strong. Bob's baking soda + vinegar will at least get some bubble action down in the cracks and neither the acid or base is strong enough to do any real damage. If there is no water in the oil say a prayer and have fun with that old flathead, but your idea of cleaning out the radiator is also a good idea. I guess nostalgia is in a person's head but I wish I had such a setup in my '29! You might also consider draining out the rear gear lubricant because it does "wear out" after a few hundred thousand miles; just drain the rear and the trans, flush with motor oil briefly and refill with fresh lube fluids. The motor cooling system is the most important part to clean up and drug store oxalic acid is the quick way to a clean the interior of the block but vinegar is milder.

Don Shillady
Retired Scientist/teen rodder