Here is a link to a Concours scoring sheet. Read the rest of the document regarding rules.
Generally speaking you get 50% of the points for an item if it is simply there and an original part, 25% for condition and 25% for cleanliness. So if you don't have the original radio you lose 1/2 the points for the radio right off the bat. Note that some items are worth more than others. Hose clamps are worth one or two points out of 470. It wasn't worth a 1/2 point for me to make them all compliant.
I judged at the MBCA Concours D'Elegance at Indianapolis last July and have a 1960 SL that has received a best of show.