Hopefully that data card will not take too long to obtain.
Remember, I went to look at "VIN # 0001" here in Michigan some years ago; a fleeting glimpse. Don't know how original it was. Non-standard mechanical work or other things done 40+ years ago can be deceptive because it looks so old. It was a strange situation, it was not the owner showing me the car, but the friend of the owner. It was in Manchester, Michigan. Nothing seemed right about anything with the situation or the car.
Regarding the trailer hitch, many European trailer hitches look a bit different than American style, with the ball being a uniform piece that come out from under the car; I believe they are called "goose neck" or "swan neck" and are almost unseen in the USA. Specifications for trailer hitches differ in the USA vs. Europe. Check out manufacturer Bosal's website. Given a vote, I'd say what this car has was added in the USA.
I should also note that pages 36 & 37 of "Les Mercedes Pagode" by Jean-Luc Fournier (2007) shows the image of the Plan définitif of the 230 SL--a blue print, as it were--dated 3-January-1963. Certainly by that time, and with that translation, the body was set for production. There is no additional hood bulge shown, just the defined one in the center we are all familiar with. Also, there are some very early (1963) photos of various 230 SLs in that same book and none show that secondary bulge.
One last thing about hood bulges: around these parts, (you know, where 40,000 hot rods and cruisers came from all over and cruised up and down Woodward Avenue while 1,000,000 people watched last Saturday) engine swaps and hood bulges and modifications to accomodate them are extremely common. Entire hoods with all the right bulges to accomodate engine swaps, as well as small bulge parts added to an existing hood are routine. Not often seen on Mercedes however, but the parts are there. More common in fiberglass than metal, but they are available and have been for decades.
