The BMC in my A31 is a BM50, but it is the 2 port version as it has ABS.
The biggest 3 port BMC in Nissan Australia's database is the BM50 (1"), as found on R32 GT-R N1's.
These are the part numbers:
(5) #46010-05U01 | *RB26DETT.GT-R.17 | Tokico 1" N1 Specification
(6) #46010-05U21 | *RB26DETT.GT-R.17 | Nabco 1" N1 Specification
They retail for around $530 brand new, and you'd be lucky to find a second hand one.
Cash