Any cutting compound will do the trick, including the humble and cheap T Cut.

Whether it works will depend on there being enough paint left to polish up, if it works then get a few coats of a really good wax polish on after.

This has always been a problem with red cars, even if he paint has lost some of its laquer getting it all one colour and shiny will improve it no end.

If paint has turned genuinely 'white' then it sounds to me that the red coat has gone from those areas. Paint that is still a dull pinkish-red may come back with T-cut or the like, but you won't get a decent-looking car if any of it is down to 'undercoat' without repainting.

Not sure what you mean by 'scabby' - incipient corrosion? As has been said, 70s and 80s red cars often lost their shine in sunlight, sometimes not helped by eager polishing.