Gearbox Numbering.
As I understand it , the F refers to rear wheel drive boxes and R to Front wheel drive boxes. This can be followed by an S for double synchro boxes. The next number is the number of forward speeds. This may be followed by C or W, referring to wide or close ratios. The next number such as 56, 60, 63, 71 or 30 (short for 130) is the distance between input shaft and countershaft centres.

A, B, or C is the evolutionary series for the box as they get older. Some boxes have an L suffix for long extension housing versions. Direct drive boxes have a "direct drive" suffix after the box numbers.

56 series boxes come in 4 speed, 5 speed overdrive (rarely), and direct drive option boxes. These are the stock A series boxes from (1000's ???) 1200's 120Y and sunny's and the nismo sports option boxes.

A F4W56L is a rear drive 4 speed wide ratio 56 series box with a long extension housing.
A F5C56A from a 120Y and 310, is a rear drive 5 speed close ratios 56 series box version A .

On F5 60A boxes they can come with a # symbol after the 60A. This is to identify different shift patterns and gear size changes. Eg - dogleg shift early 60A boxes and conventional 5th over reverse late boxes.

63A series boxes were fitted to the 180B SSS, 200B SSS, Stanza SSS. They were also behind some A series in the US and Japan. These are the "super A" boxes. They can take 200 hp without stress if not subjected to high shock loads. Ideal for turbo A15's etc

71 series boxes first started behind Prince engines and had detachable bell housings on the front of the casing before the sandwich plate.. They were used on roadsters, early Z's and 240C in 4 & 5 speed models. All had Porsche style steel synchro rings. They were known as 71A boxes. In about 1971 these boxes lost their detachable bell housings, got bigger bearings, better gear profiles and became 71B boxes. These were used in all 6 cylinder applications through to 1984.

In 1984 the FJ20T engines in Skyline and S12 got a modded 71B box with larger bearings in the 71B housings. This became the 71C box when a new shifter mechanism was added to the larger bearings.

The first 71C boxes appeared behind Z24's in Navara utes, also in 300C wagons in the UK and 300ZX's both behind VG30's. A bit later they were used for a very small run behind the updated S12 behind CA18DET's.

The 71C