How to visually determine between a 915 and a 930 trans axle? Options

[HalfMoon]

I'm trying to determine from this image just what box this is?

[HalfMoon]

Research indicates the first number (7) indicates it came from a series 911 car thus making it a 915 trans axle, the second number (1) is the gear ratio's (still trying to determine what that code number means), and the third number (5) indicates it's a 1975 box. The last four numbers are the serial number.

Seems to be some confusion about the second number (1) and the first number (7).

Some say the first number (7) indicated an #03 box witch means it has a 5 sp w. optional ratio's and some say the second number (1) means it's a 5 sp standard ratio's

What those "optional ratio's" might be, I have no clue.

If it's a standard ratio then-
75-79 5 speed
915/40, 915/43, 915/44, 915/60, 915/61,
1st gear 11:35
2nd gear 18:33
3rd gear 23:29
4th gear 26:26
5th gear 28:23
Final Drive 8:31

Anyone verify?

Also from Here´s info from Tech spec book 1st edition (5/1973) for decoding the second number of ´73 transmissions:
(and keep in mind we've already identified this as a 1975 box so the following may be irrelevant)
The 2nd number designation (1) number stands for
"1 five speed standard ratio 5 sp, with oil pump and ground gears (915/00) 0001-5000 OR with shaved gears (915/01) 5001 -9999"
According to the casting number the one we're examining is a OR casting.