I've just looked at my screws. The top screw is about 5/32" long and is longer than the lower screw by about 15 thou. However i don't think these screws are the original. The upper hole is about 7/16" deep while the lower hole is 3/16" deep. The lower screw has been cut down from a longer screw, while the upper screw looks unaltered. My head is a 2JB.
The screws could definitely be different lengths, in contradiction to my manual. But it wouldn't be the first time the manual has been wrong.
Andrew