I do not have the '76 either, but do have the '73.
Table 23-A on page 135 shows 50 psf for private pleasure car storage with a concentrated load of not less than 2000 pounds without uniform live loads. Note 3 of the table refers you to section 2302(b) for the concentrated load.
The same table shows 100 psf for general storage and/or repair with the same reference foir the concentrated load. However, the same note, since the vehicles may be other than pleasure cars, to use the greater of 2000 pounds, or 40% of the gross weight of the maximum vehicle size to be accommodated.
Since this code is before '76, and is similar to '79, the '76 is probably the same. You can tell if the '76 was different than the '79 by the vertical bars placed by the side of the paragraphs changed. If you like, I can scan and post the pages for you to read.
Mike McCann
MMC Engineering