The Wiki says,

H150
The Hitachi H150 was fitted to B210s and B310s with A14 and A15 engine. It can cope with more torque than the smaller H145.
Ratios from Nissan North America:
1975-1979 4sp and auto: 3.889
1975-1979 5sp: 3.70
B310 1980: 3.889 (Auto & all A12A)
B310 1980: 3.70 (A14 manual)
B310 1980: 3.545 (A15 manual)
Datsun Competition (later Nismo) used to sell various ratios: 3.545, 3.7, 3.9, 4.111.
For 1980 and newer vehicles, look at the engine compartment build plate. It will list whether you have an H150B (HB) or regular H150.
HA38 - 3.889 ratio
HB37 - 3.700 ratio

Which doesnt seem to mention the H150A

Am I right thinking there are three H150's a standard an A and a B?

or is the standard also known as the A?

The car in the avatar is my 69 2000.