The car in the picture just had the clearest view of the rear bumper - I don't know the serial number. The pictures I have of 766 are confusing: two are of the car owned (at least at one point) by Rick Russo in your neighborhood. That one looks like a stock 'US 74 but with 17" BBS wheels. Another car in a dealer ad was claimed to be 766 also, but it had a Euro bumper conversion and the original style flat hubcaps. It was also darker, but could have been the indoor lighting. The car above seems to be a completely stock '74, though like Rick's, it has a light interior. Regarding cooling, I have only a vented one to look at, but I see that the area behind the radiator on the bottom of the car is also open. That would have provided an air exit on the non-vented cars.